The RPM Threshold

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  • Last Post 16 January 2016
Larry Gibson posted this 04 January 2016

1. For the type of minor wrinkle or rounding that most of us reject what is the rpm where it causes a significant group enlargement. I asked this because it has been suggested that there is some kind of threshold which Vaughn's work doesn't imply.

2. Does anyone know of any testing that answers the above question or indicates that long distance magnifies the deflections caused by defects beyond a proportional to distance effect. Higher RPM does increase the deflection by defects. I have been conducting numerous tests over many years to answer just that question. Be advised there are 3 chapters to this tale. I’ll not engage in any discussion until I get all 3 posted. They are posted on the CBF forum and I am copying them here. The pictures and graphs have to be converted to .png to post so it takes some time…..so be patient before you begin question. The answers to most questions will be found by the time the 3rd chapter is posted. See attached pdf of tests. 

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Larry Gibson posted this 05 January 2016

Here's the M43 data print out from the test of the M118 (unaltered). The next is the 100 yard target of the balanced (unaltered) M118 and the unbalanced (altered) M118. Plain to see how inducing an imbalance in the bullet decreases accuracy.  I would show the 200 yards targets but suffice to say the unaltered M118 shot a very nice group right at 4” demonstrating linear expansion.  The altered M118 did not keep the 10 shots on the target (backside of a 100 yard military target - 23” x25") with 4 misses. That demonstrated non-linear group expansion as the range increases. LMG    

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Larry Gibson posted this 05 January 2016

M118 Target

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onondaga posted this 05 January 2016

LMG Interesting approach. Thank You. My particular Ballistic OCD just loves it when somebody else does the work. When I deduct what I consider truth from the work of  someone else, I have no moral guilt copying it from anybody. I don't go near any RPM threshold and have never had bullets fly apart. Reasonable recommendations from Lyman and Lee completely avoid that. My Rule: Spin bullets fast enough and they will hover if they are strong enough. I didn't write this for you to comment on before  you post Chapter 2. I did it for everybody else. Gary

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Ken Campbell Iowa posted this 05 January 2016

when i wuz programming i hated people that after i worked a complicated app into a beautiful creation indeed .... would add a function that was not in the original worksheet ....

so i will with much regret forward a request that results from channeling frank marshall .... and maybe harry pope .... and wonder what would happen if the unbalanced bullets were all oriented in the chamber the same ... ?

i most humbly apologize and realize that this has little to do with a professional scientific analysis of the unbalanced mass effect .... but dr. mann would say that the group might be about the same as the more perfect bullets ... but would they still be more than twice as large at double the range ??

your efforts in the furthering of our understanding of these naughty cast bullets are both very interesting and i am sure extremely appreciated . we will happily look over your shoulder and try to learn along with you.

thanks.

ken

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frnkeore posted this 05 January 2016

My first question regarding the testing is, who will the unbiased person be, doing the blind testing?

The second is why aren't we doing this testing with one rifle using 3 barrels of the same chambering (same reamer), contour and length?

Will there be at least four 10 shot groups with each powder charge, in each rifle?

Will we get at least two 10 shot groups, fired at 200 yds with each load, to get some idea of “linear expansion” of the grouping?

As JoeB would say, we gotta have data.

Though a lot of welcome work, I look forward to the scientific results.

Frank

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Ken Campbell Iowa posted this 05 January 2016

one simplification in testing that would expedite fact-finding

is that

small groups often are part of a larger group. but large groups are not likely part of a smaller group .

so especially when mean radius is used, large groups don't need as many shots to be highly significant . i think .

ken

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Larry Gibson posted this 05 January 2016

Test Chapter 2; RPMTest; a tale with three twistsChapter 2;Test1 [311291 of 2/1 alloy]Yesterday broke clear with the promise of some warmth and little wind so I packed up the three rifles, the M43 PBL, the test ammo and the usual other necessary accouterments for the range and set off the Tacoma Rifle and Revolver Club to conduct the first test. The primary goal of this test was to see if we could determine what causes the 311291 cast bullet to loose accuracy at a certain level. On arrival at TRRC I proceeded to set up. The benches there are very solid benchrest designed and made. It was about 46-48 degrees in the shade of the firing line but was into the 50s in the sunshine. Wind was coming out of 11 oclock at 1-3 mph. The target distance was 103 yards. The testing was begun using the 10 twist rifle and then the 12 twist rifle and finally the 14 twist rifle. The barrels were cleaned between every two 5 shot groups with 2 foulers fired before testing was resumed. All data was collected via the M43 using pressure recording, muzzle screens and down range screens. Besides information on the rifle, load and test conditions the M43 provided data on the following information; Data recorded for each shot; see attached pdf.

 

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Larry Gibson posted this 05 January 2016

That has long been a standard for cast bullets. As mentioned in Chapter 1, the cases for all three rifles were fire formed to the specific rifles and “match prepped” as such. The primers used are WLRs. Two powders were used. H4895, a medium burning powder, was used with a Dacron filler in 2 gr increments from 26 gr to 38 gr. This was expected, and did, to give velocities from 1700 fps or so up through 2500 fps.

The second powder tested was H4831SC, a slow burning powder, loaded in 2 gr increments from 40 to 46 gr to give from 90 to 100% loading density. The only sorting done with the 311291 bullets were to inspect them for wrinkles, voids of non fillout. None were weighed for segregation by weight.

The gas checks used were Hornady". They were pre-seated with the Lyman GC seater on a Lyman 450 with the .311 H die and then lubed in the .310 H die. The lube used was Javelina. At no time during the  test  was there any indication of leading or “lube failure".   All told in  Test  1 I fired 75 shots for record plus 10 foulers through each rifle for a total of 250 shots. After returning home it seemed a daunting task to sort through the data, measure groups and put it into some format that is easily presented on this forum. I could list all sorts of numbers in various manners but that would just get confusing. From the listed data the M43 provides on each shot plus the averages let me tell you I've got lots of numbers! I decided instead to put the pertinent data onto graph form.

That is a “visual" way to present information and it gives valid comparisons which are easy to see and make comparisons from. It is easy enough to pull additional information of the graphs if you want it. However the little squares of the graph did not scan well so if you want some specific information don't hesitate to ask. I couldn't get the graph on this computer to work right so I resorted to graph paper and hand plotted them.    Without further ado we might as well get to the meat and potatoes of this  test  . Graph #1 is a comparison of velocity and pressure. There was considerable consternation from some forum members that pressures would not be “exact” between the rifles. I stated that, disregarding the fact that there is always variation of pressures, even with the same load in the same rifle; the pressures need not be the same in each rifle. In fact they were not. When we graph out the velocity/pressure of the same increasing loads out of different rifles what we expect to see is a linear relationship between them. The linear lines for each (red = 10” twist, blue = 12” twist, green = 14” twist) should run fairly parallel. This gives us a valid comparison of the time pressure curves of each rifle with the other rifles time pressure curves. That's exactly what we see in graph #1. As the pressure increases the velocity increases pretty close for the 10 and 12&” twist rifles but the 14” had some problems. We also see a slight divergence as velocity increases. This is expected as the 12 and 14"; twist barrels were longer than the 10” twist barrel so velocity increased more as pressure was increased. Thus the comparison between the rifles is valid as the linear progressions are close to the same. Were one of them radically different then it would be obvious a comparison wasn't valid. However there is a slight anomaly with the 14” twist. We could pontificate as to why and probably come up with numerous reasons, most of which would probably be wrong. So let's what the data can tell us regarding that anomaly.


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Larry Gibson posted this 05 January 2016

The answer to the velocity/pressure anomaly with the 14” twist is rather simple and is demonstrated in graph #2. The relationship between pressure and velocity is encompassed in internal ballistics so we merely need to look at that data showing the consistency of the loads, i.e. how consistent the powder burns. Consistency of a load (given a test string of several shots) is most often expressed in Extreme Spread of velocity and Standard Deviation of the combined averages of velocity. SD tells us what a load may do but ES tells us what that load did do. Since I am interested in what the load did do I compared the ES consistency of the loads with the pressure. In graph #2 the loads of the 10 and 12” twists all had ESs of 50 fps or less. That is pretty good consistency given the spread of the loads velocities of 1700 fps through 2500 fps. The 14” twist had some early problems with the powder burning efficiently. We see the ES for the 2nd and 3rd test loads was considerably higher than the same loads in the 10 and 12” twists. That accounts for the small anomaly in the pressure curve of the 14” twist on graph #1. The other, and perhaps more important, piece of information graph #1 gives us is the time pressure curve of the same loads in the different twists. Obviously the curves are pretty close together and linear. Thus the time pressure curve or acceleration is very close to the same for each rifle.

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Larry Gibson posted this 05 January 2016

Next let us consider the question; if the time pressure curves are the same then any deformation to the bullet due to acceleration will be close to the same. Thus if the deformation to each bullet is the same at the same rate of acceleration then any change to the form of the bullet will result in a change to the Ballistic Coefficient. Following that then won’t any changes to the BC be the same for each twist since any deformation of the bullet should be the same? To find the answer to that question we merely compare the BCs of the 3 different twists as the velocity increases (hence the acceleration increases and deformation of the bullet increases). Graph #3 provides the comparison of the BCs vs the velocities of each load in each twist. Let us remember that the BC in this case is a measured BC from the actual flight of the bullets not a guestimated one from some chart. These actual BCs measured the bullets ability to fly through the air efficiently. The higher the BC the less deformed and more stabilized the bullet was. It is readily apparent that the BCs stayed pretty much the same for all three twists during acceleration at all velocities and pressures. It is interesting to note that the BCs of the bullets from the 10” twist retained the highest BC at the highest velocity (acceleration). This is just the opposite what it would be as believed by some on this forum. The BCs from the bullets from all three twists stayed very close together and linear across the wide spectrum of velocity (acceleration) from 1700 to 2500 fps which obviously shows the acceleration remained constant regardless of the twist of the barrel. 

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Larry Gibson posted this 05 January 2016

So this is what we now know now about the same loads in the 3 different twists; the time pressure curve is very close to the same, the acceleration is very close to the same and the BCs remain very close to the same. 
 
Let’s now take a look at the results on target. After all what we are looking at in conducting this test is the accuracy at higher velocity and why that accuracy goes bad. Graph #4 shows us the group sizes vs pressure. Whoa there! Something is amiss….if the time pressure curves are the same, the acceleration the same and the BCs are the same; then if the groups get larger as we increase velocity shouldn’t the groups get larger by proportionally the same amount? [Note; by “proportional amount” is an amount to compare the accuracy of each twist to each other. The proportional amount factor of increase is found by dividing the increased group size by the smallest group with each rifle.] However, what we see is that the groups do not get proportionally larger as velocity increases. The inaccuracy of the 10” twist increases by a factor of 5.38 while the inaccuracy of the 12” twist increases by a factor of 3.14 and 14” twist increases by a factor of 2.08. 

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Larry Gibson posted this 05 January 2016

Hmmmmmm……pressure curve is the same, deformation of the bullet from acceleration is the same so then why doesn’t inaccuracy increase the same? Especially since graph #4 shows the group size vs pressure. But wait…there’s more (sorry, just couldn’t resist!). Doesn’t every one say that it is pressure that destroys accuracy? We do see that accuracy with all three twists is decreasing with the increase of pressure. If pressure was the only reason for the decrease in inaccuracy then the inaccuracy should be proportional and we find it isn’t. We also see a much greater increase of inaccuracy with the 10” twist than either the 12 or 14” twists. We also see the 12” twist’s inaccuracy to increase more rapidly than the 14”s inaccuracy. Again, if it was pressure that increased the inaccuracy then why doesn’t the inaccuracy of all three twists increase equally as the pressure increases? It seems there is something other than pressure adversely affecting accuracy and to a much greater extent.


Okay, let’s look at it one more way just to be fair. Graph #5 compares accuracy to velocity. Something wrong here again….that dreadful 10” twist is once again being more inaccurate by a greater proportional amount than either the 12 or 14” twists. How can this be? We know the acceleration is the same; the BCs are the same so the deformation of the bullet is the same yet the 10” twists inaccuracy is disproportional to the 12 and 14” twists. It should be the same amount of inaccuracy for each twist if pressure was the problem, right? The lines for each twist should be linear right? Yet we find the proportion of inaccuracy is not the same between the twists nor are the lines linear. Have we missed something? Is there another game afoot? We’ve a good handle on the internal ballistics. We know about the terminal ballistics as the group sizes are self revealing. But have we really looked hard at the external ballistics (the bullets flight)? We know the bullets are stable.  We know the BCs are getting smaller and the TOF gets longer as the velocity increases which is telling us there is some deformation from the acceleration. We know the 10” twist had the highest BC at the highest pressure and velocity so why isn’t it as accurate as the 12 and 14” twists? 

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Larry Gibson posted this 05 January 2016

Let us look at graph #6. It is a comparison of group sizes vs RPM. Note the very, very obvious adverse affect that the increasing RPM has on the accuracy of the 10” twist. That red line really climbs up there! Also note that area of RPM where the majority of accurate groups fall; it is in or below the RPM threshold. Also note that in or at the top end of the RPM threshold is where accuracy begins to deteriorate. 

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Larry Gibson posted this 05 January 2016

The tests with H4831SC seemed to be headed the same way but were inconclusive as top velocity was only 2287 fps with 100% loading density. The 10” twist velocity was 1928 fps through 2287 fps with groups running from 2.4” to 3.3” . RPM was 138,900 to 164,700. Conversely the 14” twist went from 1906 fps to 2265 fps. Groups ran .95” to 2.2” . RPM was 98,000 to 116,600. The highest peak pressure was 39,600 psi.M43. Thus I couldn’t get into a high enough pressure/RPM range with all three twists to make any comparison. 

I am not going to conclude that there is an RPM threshold as the test is not complete. I shall wait until I conclude the test before giving a firm conclusion. However, we see from the test so far that very firm evidence is being found to make a definite case that the RPM threshold is alive, well and readily producible. 

Note; a change of the testing direction was done after the original thread was posted. I switched from the 311291 (177 gr) to the 311466 (155 – 160 gr). The reason for the change was to increase velocity with a change to slower burning powders and to use a bullet with a design more conducive to HV accuracy.

LMG

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Scearcy posted this 05 January 2016

My question is on a tangent - but a related tangent to be sure. The 308 Winchester has pretty much pushed the 3006 out of the Production and Hunter class matches. The 3006 standard factory twist rate has been 10” universally. For some reason there have been and continue to be many 12” twist 308s being sold. Are we suggesting that this is likely a contributing factor to the 308s dominance in our factory chambered classes. Has anyone ever combed through the match results to separate the 10” twist results from the 12” twist results?

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Scearcy posted this 05 January 2016

I looked at the results of the 2015 Nationals. The 308s represented were both 10” and 12” twist. Unfortunately the Savages were 10” twist and all else was 12” twist. It appears brand will muddy the water of any comparison.

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Larry Gibson posted this 05 January 2016

RPM Test; a Tale with Three Twists

Chapter III; Test 1 [311466U]
 
The testing of the Lyman 311466U cast of linotype, #2 and 80/20 linotype/lead alloys focused primarily on the Palma rifle with the 14” twist chambered in .308W.  The reason was simple; the RPM threshold has already been established so the question becomes just how fast can we push a bullet cast of ternary alloy while maintaining useable accuracy (defined as 2 moa or less) and linear group dispersion size to at least 300 yards.  The 311466U was chosen because it has the design attributes for high velocity.  
 
This chapter is somewhat short because success at higher velocity keeping under the RPM Threshold came rather quickly and easily in the 14” twist Palma rifle.  Ten shot group sizes of sub moa to 1.5 moa became quite common at velocities between 2500 and 2550 fps.  The average ten shot group size was running right around 1.5 moa and was holding linear group dispersion to 300 yards.  I know that’s not setting any CBA records but pure accuracy was not the goal…..usable accuracy at as high a velocity as we could was the goal.  Here is a typical 10 shot group pushing the 311466U cast of #2 alloy right up to the top end RPM Threshold at 2656 fps (136,594 RPM).

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Larry Gibson posted this 05 January 2016

I received my excellent made NOE 310-165-FN (30 XCB) mould from NOE about the same time. I had ordered a 4 cavity aluminum cut for #2 alloy to drop the bullets right at .3105 to .311. That is exactly what the bullets drop at. I have to congratulate the folks at NOE for their excellent product. I also at that time had completed my search for a quality 16” twist .308 barrel that would be at least 30” long. My experience thus far with the 14” twist Palma rifle and computer calculations showed a potential velocity of 2800 – 2900+ fps was possible with excellent accuracy. The key to that would be controlling the RPM by keeping it under the RPM Threshold. Now the RPM Threshold for the 16” twist is 2666 fps to 3111 fps. The 16” twist will also stabilize the XCB bullet at 1800 fps so I chose to order a Broughton barrel with a heavy Palma contour. It took about 4 months for the barrel to be delivered to goodsteel so in the meantime I conducted extensive testing of the 30 XCB bullet in my .308W Palma rifle with 14” twist barrel 27.6” long. Initial testing of the 30 XCB bullet showed excellent accuracy potential at high velocity immediately.

See attached pdf.

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Larry Gibson posted this 05 January 2016

Shooting through two sets of screens simultaneously takes a bit of getting used to and I had a few “called” shots in the first couple test strings.  I had to get over the tendency to look at the screens instead the aiming point.  I shot the 1st 5 shots with the starting load on a different target to make sure of the zero.  Still, until you get used to it threading the bullet through all those screens, especially the down range screen opening which looks awfully small from 100 yards.  Those 1st 5 shots went into 1.1” which was looking good.

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Larry Gibson posted this 05 January 2016

The start load of 45 gr AA4350 started out very well though I pulled 2 shots “down and away” 
Total group size was 2.45”  with the 8 good shots in 1.6” .
The start load of 45 gr AA4350 started out very well though I pulled 2 shots “down and away” . 
The unforeseen problem was the psi 40,300 which is close to the top end for cast bullets of this alloy for best accuracy.
Obviously the full length bearing surface and minimal lube groove width had increased the psi.
The muzzle velocity was 2480 and the measured BC was .246. 
The 46 gr test load gave 42,500 psi, 2531 fps and a BC of .233.
The group size was 2.25”  with one for sure called down and away and another very good probable.
The 47 gr load, which I was anticipating to be the “accurate load” , did not disappoint me.
I put 8 of the 10 shots into 1.2” .
Two shots went high and were not “calls” ” ¦.all 10 shots were good shots.
Looking at the data I see those 2 shots (#7 & #9) were high end velocity wise (#7 was the high velocity) and both shots had the low end BCs” ¦.pretty low actually.
That indicates something was wrong with, or happened to those 2 bullets.
Give equal velocity the lower the BC the less stable in flight.
The muzzle velocity for this load was the desired 2605 fps but at 45,500 psi!
The BC was .231 and would have been higher except for those 2 low ones of #7 & #9 shots.”

 

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Larry Gibson posted this 05 January 2016

The 49 gr load, which was slightly compressed, was also somewhat surprising in that the group did not open further considering the 2686 fps muzzle velocity and the 50,700 psi!  The group was a decent 2.5” . The BC again showed an increase to .249.  
 
To say I was surprised and very pleased with this bullets performance would be an understatement!  I do believe this NOE 311-165-FN is a definite winner.  What I have to do now is to get the psi down to around 40 – 41,000 max with a velocity of around 2600 fps in this .308W Palma rifle.  I also tested some 173 gr modern SIL cast bullets Tim sent me loaded over RL22. Pressures were less at close to 100% load density. With this NOE bullet over RL22 the psi should be down around a manageable 40-42,000 psi at close to the projected 2600 fps.  
 
That is where my next test will take me.  I also will reshoot the 47 gr load of AA4350 just to confirm whether it is a good load or not.  With the 30x57’s (30 XCB) larger case capacity it should be able to keep the psi’s down even better.  
 
By the way; I did not clean the barrel between test strings.  After the 56 round at these high psi’s and velocities I ran a wet patch down the barrel and found no trace of leading or fouling.  The lube groove sizes are sufficient and the 2500+ is doing an excellent job.
 

Again keep in mind here I am pushing the bullets as hard as possible with the goal of useable accuracy not the best accuracy.  Once we find out how fast we can push a ternary cast bullet with useable accuracy we can then begin refining that to improve upon the accuracy.  What we did find was excellent moa and better accuracy at 2467 fps and at 2490 fps. fps.  

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Larry Gibson posted this 05 January 2016

49 gr load

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Larry Gibson posted this 05 January 2016

Further testing for consistency and accuracy has produced with boring regularity an average group of 1.25" with a velocity of 2700+ fps.  Some 10 shot groups are under moa and some stretch out to around 1.6 moa while maintaining linear dispersion to 300 yards.

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Larry Gibson posted this 05 January 2016

So the question arises of how do we push the RPM threshold up and how far can we push it?   I have just completed a test of the NOE 30 XCB bullet in 10” and 12” rifles.  Was it a complete test? No.  Did I seek the best accuracy? No.  What I did was push the XCB to high velocity while maintaining acceptable accuracy where most all other cast bullets lose accuracy.  Before we get into the test results let me explain the test parameters. The rifles: the 10” twist rifle is a M1909 Argentine made M98 action with a 24” Adams & Bennet barrel having a 10” twist and chambered in .308W.  The barreled action is bedded in a wood sporter stock (Churchill Arms, England).  The action has not been trued.  The chamber was finish reamed to minimum headspace with a Clymer M118 Match reamer.  The rifle shoots right around 1 moa (10 shot groups) with selected match loads using 168 or 175 Sierra MKs. The rifle has an old original Weaver K-10 scope on it. The 12” twist rifle is a M70 Heavy Varmint rifle with a 26” factory barrel on it.  It has been pillar bedded and a rail put in the fore end for a hand stop.  It is a very accurate rifle and shoots ½ moa with 175 MKs.  I have “cleaned the 600 yard line several times with it and the 1000 yard line a couple.  For testing it has a Redfield Ultimate 4x12 scope on it.  The 30 XCBs were cast of Lyman #2 alloy and WQ'd out of the 4 cavity aluminum NOE mould.  The BHN runs 22 ”€œ 24.  They drop at .3105.  The bullets were visually inspected and any visible defect rejected the bullet.  The visually passed bullets were then weight sorted to +/- .1 gr.  Hornady GCs were crimped on using a .311 H&I die in a Lyman 450 with the GC seater used.  They were then light lubed with a spray lanolin lube and pushed through a Lee .311 sizer to fully crimp the GC on.  The GC'd bullets were then lubed in the .311 H&I in the 450 lubrasizer and lubed with 2500+ lube.  Fully dressed the bullets weighed 164.7 gr. Cases were match prepped LC Match. Primers were WLRs.  Cases were fire formed and neck sized with a Redding Bushing die to give just a slip fit over the NOE M die expander (a very neat tool BTW) for Lee case mouth expander die.  Already knowing which powders gave the best high velocity accuracy with the Lyman 311466 and the LBT 30-160-SP bullets in both rifles I chose to use the same powders under the NOE 30 XCB bullet.  That would give a good comparison.  Thinking the NOE 30 XCB should withstand a bit higher acceleration each powder was loaded over the point where the Lyman and LBTs went over the RPM Threshold and lost accuracy.    That brings up “accuracy”.  The objective of this test and the other XCB tests was to push to the highest velocity possible while maintaining 2 moa or less accuracy with linear expansion at 200 and 300 yards or further for 10 shot groups. Why 2 moa?  Because that is the useable accuracy criteria those of us running these tests chose. The 2 moa criteria has been the high power standard for many years.  You can kill deer, coyotes and such all day long with a 2 moa rifle.  Some have a hard time with “useable” and seem to grasp “reasonable” as a good measure.  The two mean the same.  That criteria was chosen because the primary objective is high velocity with accuracy.  Once we find out the upper end of velocity with one set of components that maintain 2 moa or less then we can tweak the load and components for best accuracy, if we want to.  All velocities (muzzle) were measured with the Oehler M43 PBL.  For each shot the screened velocity was recorded along with a “proof”, a pressure trace was recorded and the peak pressure and associated Area and Rise of the pressure were recorded.  The averages of velocity and the pressures along with their SD & ES were computed.  The screened velocity was converted to muzzle velocity. On the data sheet for each test string I traced the bullet holes, measured group size (ctc) for record and computed the RPM. Most of the test strings are of 10 shots but 3 have 9 shots (out of 20 test strings).  I also tracked each shots location on the target and numbered each bullet hole on the data sheet accordingly.  This gives a very clear understanding of what is happening during the internal ballistic phase.  This test produced 20 data sheets (both rifles) so I will not post them all.  I will post the pertinent ones that show the top end capabilities of the NOE 30 XCB as tested in each rifle. For those enamored with 5 shot groups it is interesting to note that in tracking the shots on target in 7 of the 20 test groups the first 5 shots went into less than 1 moa (1 in the 10” twist and 6 in the 12” twist).   Thus, based on 5 shot groups, we could claim that 35% of our groups were “sub moa” and thus our loads were.  However in doing that we would only be fooling ourselves. I have often stated the RPM Threshold (120,000 ”€œ 140,000 RPM) is not a “limit” but could be pushed up.  I have said two of the prerogatives for doing so is to use a slower burning powder to slow the acceleration rate and to use a properly designed cast bullet of appropriate alloy to with stand that acceleration rate.  The NOE 30 XCB bullet was design expressly for high velocity.  It is succeeding exceedingly well at 2600 ”€œ 2800+ fps in 14” twist barrels.  Let us see how well it does at higher velocity and RPM in the 10 and 12” twist rifles. The 10” twist rifle (24” barrel) results; I chose two powders to test under the NOE 30 XCB bullet in the .308W rifle with 10” twist; RL19 and RL22.  Both of those powders gave the best accuracy out of this rifle with the Lyman 311466 and LBT 30-160-SP cast bullets.  Both of those bullets began going over the RPM Threshold at about 2300 fps/165,000 RPM with RL19 and about 2350 fps/169,000 RPM with RL22.  Note how both of those bullets and powders have pushed up the RPM Threshold over the incorrectly assumed “limit” of 140,000 RPM.  Both of those bullets held under 2 moa accuracy with linear expansion at 200 yards.  Thus with that baseline to measure against I loaded test strings of 38, 40, 42, 44 and 46 gr of each powder to test the NOE 30 XCB bullet. The 38 gr load of RL19 gave 1938 fps, 139,536 RPM at 28,100 psi(M43).  The group size for 9 rounds was 1.2” (I excluded the 1st shot out of the cold clean barrel which always drops low out of the group).  Shots 2 through 6 went into .85”.  The ES was 146 indicating that RL19 does not ignite and burn efficiently at this pressure.  A dacron filler probably would have helped that but no filler was used. The 40 gr load of RL19 gave 2075 fps, 149,400 RPM at 31,100 psi(M43).  The group size was 1.5”.  The ES immediately tightened up to where it should be.  In fact this test strings ES or 37 fps and SD of 11 fps were excellent. The 42 gr load of RL19 gave 2194 fps, 157,968 RPM at 35,000 psi(M43).  The group size was 1.65” The 44 gr load of RL19 gave 2313 fps, 166,536 RPM at 38,900 psi(M43).  The group size was 1.55”.  Again an excellent ES of 30 fps with the SD at 9 FPS.  The Pressure ES was 1,200 psi with an SD of  400 psi which is excellent and demonstrating excellent ignition and uniform burn. 

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Larry Gibson posted this 05 January 2016

The 46 gr load of RL19 gave 2434 fps, 175,248 RPM at 43,700 psi(M43).  As with the much slower 14” twist rifle I am finding the psi of 41,000+ to be very hard on cast bullets of this alloy.  We see while the group size is 1.9” there are 2 and probably 3 flyers telling us that this load is exceeding the RPM Threshold or, at least those 3 shots were.  Dropping the load to 45 gr would probably give close to 2400 fps at 41,000 or less psi and still give us the 1.5 +/- accuracy level wehave achieved with the other loads.  That is a 100 fps +/- increase over the Lyman 311466 and the LBT 30-160-FN bullets in this rifle with RL19.  That is indicating the NOE 30 XCB bullet is indeed holding up better under the high rate of acceleration and RPM generated in this 10” twist rifle.

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Larry Gibson posted this 05 January 2016

Moving on to the RL22 results; the 38 gr load of RL22 gave 1944 fps, 139,968 RPM at 27,800 psi(M43).  The group size was 1.5”.  The ES and SD were still high at 80 and 26 indicating the RL22 was not burning efficiently at this psi. The 40 gr RL22 load gave 2037 fps, 146,664 RPM at 30,000 psi. The group size also was 1.5”.  Again the ES and SD were high at 94 fps and 27 fps.  The 43 gr RL22 load gave 2132 fps, 153,504 RPM at 32,600 psi(M43).  The group size was 1.45” and the ES and SD tightened up to 44 fps and 17 fps.  This indicates the RL22 is burning efficiently at this psi. The 44 gr RL22 load gave 2267 fps, 163,224 RPM at 37,300 psi(M43).  The group size was 1.3”.  The ES and SD remained low at 57 fps and 19 fps.  The 46 gr RL22 load gave 2381 fps, 171,432 RPM at 41,800 psi(M43).  Again the ES and SD remained constant at 62 fps and 20 fps.  This load might be increased to 47 gr with a 2400+ fps velocity and remain under the RPM Threshold.  If accuracy holds at 1.3 - 1.5” moa and remains linear at 200 and 300 yards it would be a very useable load for a 10” twist .308W.  as it is the 44 and 46 gr loads are both quite useable.  Might even do a bit better in a larger capacity 30-06.

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Larry Gibson posted this 05 January 2016

46 gr RL22

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Larry Gibson posted this 05 January 2016

Moving on to the RL22 results; the 38 gr load of RL22 gave 1944 fps, 139,968 RPM at 27,800 psi(M43).  The group size was 1.5”.  The ES and SD were still high at 80 and 26 indicating the RL22 was not burning efficiently at this psi. The 40 gr RL22 load gave 2037 fps, 146,664 RPM at 30,000 psi. The group size also was 1.5”.  Again the ES and SD were high at 94 fps and 27 fps.  The 43 gr RL22 load gave 2132 fps, 153,504 RPM at 32,600 psi(M43).  The group size was 1.45” and the ES and SD tightened up to 44 fps and 17 fps.  This indicates the RL22 is burning efficiently at this psi. The 44 gr RL22 load gave 2267 fps, 163,224 RPM at 37,300 psi(M43).  The group size was 1.3”.  The ES and SD remained low at 57 fps and 19 fps.  The 46 gr RL22 load gave 2381 fps, 171,432 RPM at 41,800 psi(M43).  Again the ES and SD remained constant at 62 fps and 20 fps.  This load might be increased to 47 gr with a 2400+ fps velocity and remain under the RPM Threshold.  If accuracy holds at 1.3 - 1.5” moa and remains linear at 200 and 300 yards it would be a very useable load for a 10” twist .308W.  as it is the 44 and 46 gr loads are both quite useable.  Might even do a bit better in a larger capacity 30-06.

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Larry Gibson posted this 05 January 2016

The 43 gr H4831SC load gave 2159 fps, 129,540 RPM at 27,100 psi(M43).  Nothing spectacular at 1.8” group. The 45 gr H4831SC load gave 2289 fps, 137,340 RPM at 30,800 psi(M43).  Another ho-hum group at 2”.  Now the 47 gr H4831SC load was getting there at 2415 fps, 144,900 RPM and 34,500 psi(M43).  The 1st five shots went into .7” with the 10 shot group at 1.34”.  The ES and SD were very good at 33 fps and 11 fps.  This powder also needs to be tested at 48 and 49 gr in this M70 12” twist rifle.  The Oehler M43 PBL for the 47 gr H4831SC load;

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Larry Gibson posted this 05 January 2016

The 43 gr RL22 load gave 2153 fps, 129,180 RPM at 26,800 psi(M43).  The 1st five shots went into .93” with the 10 shot group at 1.7” The 45 gr RL22 load gave 2273 fps, 136,380 RPM at 30,200 psi(M43).  The group was 1.4” The 47 gr RL22 load gave 2398 fps, 143,880 RPM at 34,100 psi(M43).  The 1st five shots went into .55” with the 10 shot group in 1.6”.  This powder also needs to be tested at 48 and 49 gr in this rifle.  The Oehler M43 PBL for the 47 gr RL22 load;

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Larry Gibson posted this 05 January 2016

The last test was just 1 load with LeveRevolution powder.  I took a guess and figured 40 gr with a .3 gr Dacron filler should give around 2500 fps.  I came pretty darn close!  The 40 gr load gave 2510 fps, 150,600 RPM at 31,900 psi(M43).  The 1st five shots went into .8” with the 10 shot group at 1.5”.  The ES and SD were outstanding at 21 fps and 7 fps. 

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Larry Gibson posted this 05 January 2016

So there it is, you can push the RPM Threshold up just as I have said with faster twist rifles.  There is a plethora of 10 and 12” twist .30 caliber rifles out there.  They are “regular” rifles.  So if anyone wants to shoot higher velocities with them and maintain useable/reasonable it isn't that difficult as I have shown.  First of all you and your rifle need to be capable of the accuracy you want.  You must know how to cast quality bullets of proper alloy.  You need to use appropriate slow burning powders and you need a cast bullet designed for that purpose.  The NOE 30 XCB is the bullet for the job.   LMG     So what does this “Tale of Three Twists” have to do with John's question?  Let's refresh that question in our minds here;    "1. For the type of minor wrinkle or rounding that most of us reject what is the rpm where it causes a significant group enlargement. I asked this because it has been suggested that there is some kind of threshold which Vaughn's work doesn't imply.     2. Does anyone know of any testing that answers the above question or indicates that long distance magnifies the deflections caused by defects beyond a proportional to distance effect.  Higher RPM does increase the deflection by defects."   The “Tale” gives the answer to “it has been suggested there is some kind of threshold".....and indeed there is.  It is an RPM Threshold.  The testing definitely proves that the defects do magnify the deflections, especially after the RPM Threshold is crossed by the evidence of larger groups and non linear group expansion as the range increases.  A lot of further testing has been done since this “Tale” was written.  The 16” twist rifle has been built and tested with amazing results.  It s chambered in slightly larger capacity 30x60 XCB cartridge and is delivering the same 1 - 1.5 moa accuracy at the expected 2800 - 2900+ fps.  Testing continues though.   LMG

 

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frnkeore posted this 05 January 2016

Although this sounds new, it's mostly <2008 info, cut and pasted to this thread. Larry has added some new text to it. It's a long thread but, this is it:  

  http://castboolits.gunloads.com/showthread.php?245302-RPM-Threshold-A-Tale-of-Three-Twists-Chapter-II>http://castboolits.gunloads.com/showthread.php?245302-RPM-Threshold-A-Tale-of-Three-Twists-Chapter-II 

  Many here, have read it when it was first going on.   This will be the first of many question, regarding this subject, some copied and pasted from the other thread.     “The RPM threshold maybe lower than 120,000 RPM, with very fast powders”   Are we talking B'eye, Unique, 2400, 4227, RX7, 2015, or 3031? Where does it start? I edited the other obvious factors out. I want to know about this one.   

If the bullet isn't damaged, as your graph shows, how does the burn rate effect the “threshold", by itself? Will your “threshold” stand if fast powder, well cast, hard (enough) bullets and load them properly?   

Frank

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Larry Gibson posted this 05 January 2016

Frank

Yes the faster burning pistol powders will lower the RPM Threshold of a particular cast bullet in a particular cartridge. With the medium burning powders given an appropriate weight bullet of appropriate alloy and BHN the RPM Threshold will fall in the listed ranges. It's with the slower burning powders (as posted in this thread) that the RPM Threshold can be raised.

The reason is the faster burning powder has a faster “rise to pressure” than the slower burning powder given the same psi i.e. it kicks the bullet harder quicker even though the velocity is lower. Just as I lowered the RPM Threshold of the jacketed bullet M118 bullets by unbalancing them the RPM remained the same. It's the same with the lower end of the RPM Threshold. It can be lowered still by faster burning powders that cause more imbalances in the bullet. Had you actually read what was posted a long time ago about the RPM Threshold stated as 120 - 140,000 RPM you would have known that.

Also I gave no time line for the tests conducted for this topic. Actually I cut and pasted here from the articles I wrote on the subject the same as I did on the other forum.  You seem to be the only one who is implying I did all the testing yesterday just for this article? I didn't and didn't say or indicate I did.  Of course I cut and paste, did you really expect me to have typed it all over again? Or is it that you're not here for the party?

LMG

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Larry Gibson posted this 05 January 2016

Here is another example of a test conducted demonstrating the adverse affect of imbalances in cast bullets and what happens (non-linear expansion of the group as range increases, especially past 100 yards) when the RPM Threshold is exceeded.   The test load was the 311291 cast of COWWs +2% tin.  The bullets were AC'd and aged 10+ days.  They were visually sorted for defects with those rejected.  The bullets were not weight sorted.  GCs were Hornady's and the lube was Javelina or 2500+.  The loads (using 4895) were not worked up for accuracy but was simply selected as those below the RPM Threshold and the other above the RPM Threshold.  Rifle was my test .308W with a 24” barrel and a 10” twist. The test was 10 shot groups with each load at 50 yards, 100 yards and 200 yards. As we see from the 1st picture with the 28 gr 4895 load (1894 fps/136,368 RPM) we have a 50 shot group size of 1.25” with a .7” main cluster.  The 100 yard group is 1.55” with a 1.3” cluster. The 200 yard group is 4.25” with a 2.5” cluster.  Essentially linear expansion of the group size from 50 yards to 200 yards. LMG

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JimmyDee posted this 05 January 2016

An excellent write-up.

Thank you for taking the time to share your results with us.

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Larry Gibson posted this 05 January 2016

The 38 gr 4895 50 and 100 yard groups.

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Larry Gibson posted this 05 January 2016

The 38 gr 4895 200 yard group.

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Mike H posted this 05 January 2016

LMG,       Thanks for posting that.Mike.

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frnkeore posted this 06 January 2016

Party? Where is the party. Do we get food and refeshments? I'm down for that :)

On a more serious note.......... So what your saying is that fast burning powders “unbalance” bullets?

How is that done? Is it by distortion? Are the bullets “bent” or collapsed or some other way of unbalancing them?

Will a very short nose or a wad cutter, become less unbalanced and shoot more accurately, than say the XB bullet, with fast powder?

Do you have recovered bullets to show how they got unbalanced? Or is it just assumed that fast powder unbalances bullets?

Frank

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frnkeore posted this 06 January 2016

This is a picture of the muzzles of the three rifles but, could we get a full picture of them? What are the particluars for each of the rifles? Twist Barrel make Land and groove diameter Number of grooves for each barrel and the lands width How old are the barrels, how many jacketed, high pressure bullets have they each fired. Why wasn't the same scope, used on all the rifles? That will be all NEW info, not given before. Frank

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goodsteel posted this 06 January 2016

Hey Frank, would you be willing to help with setting up three identical rifles for side by side testing? I am totally convinced that 99% of what LMG has posted here is solid as a rock (with the one exception of the cause of the RPMTH being due to damaged bullets. He knows I differ on that point). I am very very sure that three rifles of adentical barrel makeup will perform exactly as LMG says, mainly because I have built two twitch barrel rifles with three barrels of different twist rate for gentlemen who shoot HV cast bullets, and the results back up the RPMTH exactly, especially in 30 caliber. It's a very fun pursuit, and you can't believe the amount of information you can gather from a rifle like that.

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frnkeore posted this 06 January 2016

Tim, In what way would you like me to help? If it involves $, I can't help. I'm retired with only SS income and that's why I'm not a CBA member (although I support the local club matches with shooting fees).

Another aspect of this is, that it was started to prove that the resulting conclusion would be his “threshold” would prevail.

This type testing takes a LOT of work, more groups shot and BLIND testing. Larry could do the loading in bulk quantitys but, a skilled, objective shooter would have to do the shooting, not knowing what twist the barrel is.

I'd be happy to help in any way that I can. I'm sure that JoeB or others with statical skills, could help with sorting the info, too.

Frank

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Ken Campbell Iowa posted this 06 January 2016

frank ... maybe you could work on one of your own questions ..... do wadcutters have a rotational threshold ? ...

i am wondering if the threshold ( assuming there is one ... ) .... is from some distortion of the bullet by the time it leaves the muzzle .... ( temporaroly dismissing distortion afer it leaves the muzzle .... although ken mollohan did bring that up ...muzzle blast ... ) ...

?? some of the distortion is from acceleration ???

?? some of the distortion is from < slumping ... melting... bad breath .... > ....

if slumping ... is it to do with some result of limit of plasticity ?? lead molecules are like little ball bearings ... not well locked together ... would hard gas checked wad cutters have a spin threshold ?? and yes you could do a few shots with a nose rider, which we all know goes berserk at high speeds ... rotational ??? speeds, that is .

and i doubt you would need anything but a chrony to collect data .... oh, and a decent deer-rifle accurate rifle . we are just looking for that point of sudden non-linearity . heh . if it is acceleration and/or slumping it wouldn't seem that a super grade match barrel would change much .... ?? a $100 midway barrel should work ... green mountain i think ...

ken

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goodsteel posted this 06 January 2016

I am 99% convinced the RPMTH exists and is very easily demonstrated by anyone who will put enough powder in the case to observe it (honestly, it's really hard to miss when your groups go from 2MOA to 10MOA very predictably in a just a few FPS increase. I mean REALLY, it's not that hard to see it if you shoot faster) and also that it is caused by the bullet getting loaded with tension caused by inertia which is released as the bullet crosses the muzzle. When the bullet is launched forward and encounters the rifling, the nose is effected by the rifling before the rear of the bullet. The nose does start to twist, and the base catches up. This engraves the bullet with a twist in its body. The alloys we use are strong enough to spring back (evidence easily observed by the way they size larger than a pure lead bullet through the same sizer) after the bullet crosses the crown.

I believe the bullet snapping back in shape suddenly as it leaves the muzzle of the rifle is what causes the RPMTH. This explains why paper patched bullets side step the RPMTH. This explains why copper jacketed does also, and this totally explains why using a slower twist barrel modifies the RPMTH so effectively. For one thing, the sudden rotation of the nose of the projectile is dampered dramatically making it so that the bullet is not as twisted in the first place, and also, when the bullet leaves the muzzle, it is spinning just fast enough to stabilize the bullet but not fast enough for centrifugal force to get ahold of it.

I believe this to be the truth behind the RPMTH. I discovered it by shooting every bullet design I own through a fast twist barrel, into a bucket of wet sand in my shop with a light load of bullseye in 30-06. I observed the lovern style bullets had rifling marks that were not even. The rifling marks looked like they were biased into a slight S shape. I concluded that this could not have happened inside the barrel, so it must have happened just after the bullet left the crown.

That's my explanation of the RPMTH, and I designed the XCB bullet to counter this effect as much as possible, and it ended up being the bullet LMG shot to 3000FPS in his slow twist rifle.

I believe this is why the RPMTH exists. Why it changes with varying bullet hardness and powder selection and twist rate.

Frank, does this answer your questions about the RPMTH sufficiently?

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gpidaho posted this 06 January 2016

Thanks for that Tim. That brightened my dim bulb. Very good explanation. Gp

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Ken Campbell Iowa posted this 07 January 2016

mr. goodsteel .... would the pope muzzle device loading ... ( down the barrel backwards ... for pre-engraving .. ) ... stop the shock-twisting as the bullet leaves the muzzle ??

i shot that system when i wuz young but my popper loads of #80 never went fast enough to reach threshold disaster ...

a dandy discussion, by the way ... up to now, i have blamed almost all the problems with cast on the bullet being distorted in the first inch upon firing .... and never thought about how the dispersion might be non-linear with the rotation .... i will put my sub-conscience visualizer to work on how the bullet might unwind upon exiting suddenly the muzzle ... so far no results ... but ...

ken

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Larry Gibson posted this 07 January 2016

frnkeore wrote: This is a picture of the muzzles of the three rifles but, could we get a full picture of them?

What are the particluars for each of the rifles?

Twist

Barrel make

Land and groove diameter

Number of grooves for each barrel and the lands width

How old are the barrels, how many jacketed, high pressure bullets have they each fired.

Why wasn't the same scope, used on all the rifles?

That will be all NEW info, not given before. Frank
And to what end is that information pertinent to the objective of the test?  The object was not to test the accuracy of one twist vs another twist.  The objective was not to test whether one type of rifling is more accurate than another.  The description of each rifle and it's accuracy capability is stated in Chapter I.  The objective of the test was also clearly stated.  This was also discussed thoroughly on the other forum.  The objective of the test was;   "I will compare the accuracy of each rifle unto itself. In other words each rifle and it's bullets flight will tell us when that rifles accuracy begins to deteriorate. The loads used in all three rifles will be the same and it is then when accuracy deteriorates in one rifle the RPM of that rifle with that load is comparable to the RPM of the same load in the other rifles."

What that simply means is we were not looking for the most accurate load.  If one rifle shot moa, the next shot 1 1/2 moa and the 3rd shot 2 moa as their best accuracy that was fine.  What we looked for was the point where accuracy deteriorated.  Specifically we were looking for the RPM rate when the accuracy of each of the rifles deteriorated.    We then compared those RPM figures and found that accuracy for all 3 rifles deteriorated very close to 130,000 - 145,000 RPM even though the velocities were 2025 fps with the 10” twist, 2275 fps with the 12” twist and 2450 fps with the 14” twist rifle.  Given what John Alexander's question was this test gives an answer.  The test was not about finding best accuracy but finding where the RPM adversely affected accuracy which was John's question.   Should you wish to assist as a couple members have suggested I also would be happy to assist.

  LMG   BTW; welcome to the party, enjoy.      

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frnkeore posted this 07 January 2016

Tim, Regarding this statement:

"I believe this is why"

With all do respect, I've heard these words before, used in many different context, even beyond shooting. If I took them as gospel, I would be even more confused than I am. Not to mention the 99%.

Is it wrong to ask for scientific proof of anything? Slap me in the face with it and I'll get on the Band Wagon.

When I provided proof that at CBA matches, Larry's “threshold” was being exceed by up to 180K RPM and that the CBA shooters where getting better accuracy than what he was posting. My info was discounted by most of the resonding people in that thread and Larry, basically said that he doubted the accuracy of the the equipment lists.

When I posted that I was only the messager (and not to “shoot” me), I was told that I should only post findings if I did it myself.

I have no interest in HV, low BC shooting as wind drift can be reduce below the HV/low BC levels with high BC bullets at standard match velocitys of ~2200 fps. Further more, using match type equipment, the HV accuracy doesn't come close to equaling CBA match results, not even in the PB class, shot at much lower velocity.

Although, I'm willing to help in any way I can, if the testing is done scientifically, my interest in pursuing my own testing will have to wait until the accuracy gets in the “match” area, with less wind drift. The recoil and expense is also a issue for me, personally.

Frank

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goodsteel posted this 07 January 2016

Ken Campbell Iowa wrote: mr. goodsteel .... would the pope muzzle device loading ... ( down the barrel backwards ... for pre-engraving .. ) ... stop the shock-twisting as the bullet leaves the muzzle ??

i shot that system when i wuz young but my popper loads of #80 never went fast enough to reach threshold disaster ...

a dandy discussion, by the way ... up to now, i have blamed almost all the problems with cast on the bullet being distorted in the first inch upon firing .... and never thought about how the dispersion might be non-linear with the rotation .... i will put my sub-conscience visualizer to work on how the bullet might unwind upon exiting suddenly the muzzle ... so far no results ... but ...

ken Ken, yes, I tested that exactly. It was part of proving my theory you see? I surmised that a rifle I had built in 30XCB with a 1-14 twist would theoreticaly be able to shoot much faster from a pope seated bullet, than shooting from fixed ammo because teh twist would be eliminated. So what I did was make a special breach seater that was powerful enough to seat a GC bullet of #2 alloy or linotype all the way into the barrel up to the GC. The rifle we used for this experiment was a known entity that was not able to shoot past 2750 accurately with it's 1-14 twist barrel which is precisely where LMG's RPMTH claimed accuracy would deteriorate. When breach seated, the rifle was able to maintain accuracy up through 3100FPS!!!!I felt that was a very big +1 to my twisted bullet theory. 

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joeb33050 posted this 08 January 2016

I've said that all of micro or macro can be put on both sides of a sheet of 8 1/2X11 paper. Others have said that if it can't be put on a postcard they won't read it. Larry, I've gone through this before, years ago, and I still can't read it without dozing off. My advice is: Write a summary, one side of a 3 X 5 card. Then go to 3 pages, 8 1/2 X 11. Then the whole megillah. 1 in 20 will continue after 3X5, 1 in 100 after 3 pages. Otherwise few to none will ever get it. 

Don't misunderstand, there will always be opinions, from folks who never read it. It's like the congress.

Opinions are like cowboy hats... or is that something else? joe b.

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Larry Gibson posted this 08 January 2016

joe b.

I certainly appreciate the comments. I have put it on much less than one side of a 3x5 card.....numerous times....no too many times and then out come the pundits with basically “that's BS, prove it.” Also many well meaning folks simply want to know how I arrived at the fact there is an RPM Threshold with cast bullets. For both of those, the pundits and those that want to know, the answer and proof are there.  Those answers won't fit on one side of a 3x5 card so I just went with the whole 3 pages. 

For those that go to sleep they only have to get through the simple definition of the RPM Threshold at the beginning. If they accept it they need not read further. If they don't they need to make a pot of coffee and continue reading as that should answer most questions.  I am, as I always have been open to discussing and clarifying any pertinent questions. 

To those who simply want to argue who ask the same questions over and over and say I don't answer their questions (the way they want to hear it answered anyway) I say; just read the tests and results and if you still disagree then please conduct your own tests to prove otherwise.  In the past several years not a single pundit has conducted any test that proves contradictory.

I noticed on another thread you asked; “Ya got 9 pages, and aside from my report, I can't find any data here that talks to the question. Lots of opinions, references to Mann and Vaughn, but no data."  So I gave you lots of data in less than 3 pages here that talks directly to John's question.  Just trying to be helpful.... 

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joeb33050 posted this 08 January 2016

LMG wrote: joe b.

I certainly appreciate the comments. I have put it on much less than one side of a 3x5 card.....numerous times....no too many times and then out come the pundits with basically “that's BS, prove it.” Also many well meaning folks simply want to know how I arrived at the fact there is an RPM Threshold with cast bullets. For both of those, the pundits and those that want to know, the answer and proof are there.  Those answers won't fit on one side of a 3x5 card so I just went with the whole 3 pages. 

For those that go to sleep they only have to get through the simple definition of the RPM Threshold at the beginning. If they accept it they need not read further. If they don't they need to make a pot of coffee and continue reading as that should answer most questions.  I am, as I always have been open to discussing and clarifying any pertinent questions. 

To those who simply want to argue who ask the same questions over and over and say I don't answer their questions (the way they want to hear it answered anyway) I say; just read the tests and results and if you still disagree then please conduct your own tests to prove otherwise.  In the past several years not a single pundit has conducted any test that proves contradictory.

I noticed on another thread you asked; “Ya got 9 pages, and aside from my report, I can't find any data here that talks to the question. Lots of opinions, references to Mann and Vaughn, but no data."  So I gave you lots of data in less than 3 pages here that talks directly to John's question.  Just trying to be helpful.... 

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Larry Gibson posted this 08 January 2016

Joe Paragraph 2 of Chapter I; “The RPM threshold is that point where accuracy begins to deteriorate when the RPM is sufficient to act on imbalances in the bullet in flight to the extent the bullet begins a non-linear helical spiral in flight or its flight path goes off on a non-linear tangent from the line of flight."

That's it “on a 3x5 card".  My apologies if you don't get it.  I can't make it any simpler than that so I guess that's my fault.   LMG

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goodsteel posted this 08 January 2016

Let me take a crack at it. If you take your Savage 308 out there and want to shoot normal jacketed velocities with similar weight bullets, but your accuracy suddenly departs at 2100 FPS no matter what alloy or powder you try, you might want to read what LMG has written if you're at all curious about why that is.

If you don't care why a cast bullet cannot easily be shot at normal jacketed velocities, and do not care to fix it with a 10 minute kitchen table barrel swap, then there is absolutely no reason to read what was written in this thread.

Not that I have any issue shooting low velocity stuff. I actually enjoy it very much. But I am not content with that. I want to be able to say I know how to shoot cast at HV, and since I read what LMG wrote and gave it a try.........I can, and have, and the range officers where I shoot have spotted for me while I did it, and shot the rifles. I'm locally famous because of this. There's always a crowd that gathers round when I'm stacking groups with lead at jacketed velocities. It's cool! It's fun! It's repeatable! and its easy to do!

Now, I'm just a gunsmith and a deer hunter, but sometimes I wonder what would happen if a real CBA competitor applied trained shooting techniques to this with an eye on accuracy. Think he might be able to do better than me with my COWW alloy? Better still, if I'm shooting 1.5MOA at 2700FPS, I wonder how I would fare in CBA competition at normal velocities? (I would actually enjoy that immensely, even when I got my clock cleaned. LOL!)

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frnkeore posted this 09 January 2016

I'm excited to hear this, Tim:

"Better still, if I'm shooting 1.5MOA at 2700FPS, I wonder how I would fare in CBA competition at normal velocities? (I would actually enjoy that immensely, even when I got my clock cleaned. LOL!)"

From what I've read of your builds, they are “match” rifles and your workmanship is good.

Get to a match, it's fun and you might become famous in CBA, also and not just your local range.

Start slow and work up a “normal” competitive load. Then work up to your HV stuff, we'd all like to know if it can be competitive. We already have guy's shooting up to 180K rpm and doing well but, at only 2200 fps.

Larry seems to be or has been a competive shooter but, he posted that he shoots a AR (jacketed)in matches at his local range. I tried to get him to shoot CBA matches when he was in WA but, he didn't want to so, I (and I'm sure a lot of others) would love for you to try it. Prove things out and let us know how it goes.

Your not to far from where they shoot the CBA Nationals and I'm sure that many CBA guys would help you get acclimated to the shooting.

I wish you well and the best of skilled luck.

Frank

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Larry Gibson posted this 09 January 2016

Excellent idea Frank, would love to shoot some CBA matches now that I have the time.  When we discussed a few years back I didn't have the time when I was in Washington because I was contracting and was away from home a lot of the time training Soldiers, Marines and CBs as there was a war going on back then.  When at home I had too many other shooting priorities to get involved in another.    However that has changed and I'm now fully retired and have the time and inclination to shoot some CBA matches.  I have PM the military rifle match director to find out what targets are use so I can work up some loads and practice but I've received no answer yet.  I'd also be open to traveling to some matches but don't know of any in the SW.  Additionally the last schedule for matches on this forum is 2013 or maybe 2014......kind of hard to make plans to shoot a match.......maybe someone can direct me to some matches?   Other than that I do shoot the local prone match (shooting this coming Sunday).  Most every one shoots F Class but I shoot Match Rifle and I do not use an AR.  I most often use a Savage Competition M112 in .223 but I have also shot the match with my M1903A1 National Match Type II 30-06.  We shoot at 300 yards with the F Class boys shooting on the 300 yard F Class target and those of us shooting Match Rifle use the NRA 300/600 Decimal Target.  In the past I competed heavily in NRA Small Bore, PPC, IPSIC and High Power (NMC, Prone Long Range and a few Palma matches).  I used all cast bullets in the PPC and IPSIC disciplines for practice and in matches.  I used cast bullets in a M1903 in quite a few NMC 100 yard reduced matches, even used an M1 carbine one time on a bet (I won the bet) with cast bullets.   I certainly would like to shoot in some CBA matches if anyone can fill me in where?  What CBA matches do you shoot in Frank?  Where?  Maybe we can shoot a CBA Match together sometime?   LMG

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RicinYakima posted this 09 January 2016

LMG,

We would really like you to shoot with us in the Military matches. The rules are posted that you can access from the CBA home page. Targets are the reduced targets for 600 SF military rifles, MR31 and MR51? Please read the rules carefully as we are not like the NRA, i.e. no match after market barrels, or custom chambers. We shoot real military rifles, not a money game you could buy your way into.

Ric

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Larry Gibson posted this 09 January 2016

Many thanks Ric.  I see only last years schedule is posted but I will email Dan Walliser over in Scottsdale to see about shooting the matches at Phoenix this year.  I've downloaded and copied the rules for the military matches so the burning question is which rifle category.......?    LMG

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frnkeore posted this 09 January 2016

I shoot a monthly CBA match in Roseburg Oregon, I shoot monthly ASSRA matches in Grants Pass, OR and I shoot a yearly, 9 day, ISSA match in Nine Mile Falls, WA.

Is there some reason that you don't shoot cast bullets in the 300 yard matches, with both your 14 twist 308 and your 03? I'm sure that they could note in the match results, that you shot cast bullets. It might even give the other guys a incentive to shoot cast, also.

Maybe even start a CBA shoot, yourself. It's a bit of work, I started the ASSRA club in GP, in 1986 and it's still going strong. But, although I'm not a ASSRA member any more (again because I conserve my money to afford shooting fees and gas) they still record my match results, found in their bi-mothly publication and forum.

Frank

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joeb33050 posted this 09 January 2016

goodsteel wrote: Let me take a crack at it. If you take your Savage 308 out there and want to shoot normal jacketed velocities with similar weight bullets, but your accuracy suddenly departs at 2100 FPS no matter what alloy or powder you try, you might want to read what LMG has written if you're at all curious about why that is.

If you don't care why a cast bullet cannot easily be shot at normal jacketed velocities, and do not care to fix it with a 10 minute kitchen table barrel swap, then there is absolutely no reason to read what was written in this thread.

I guess that this is where I lost interest in Larry's work years ago. I'm VERY glad that Larry and you are doing the research work to get HV accurately with cast bullets. Even if I don't understand the theory.

 I shoot cast bullets because it's low recoil, low noise and low barrel wear. I don't hunt, and if I did I'd use jacketed bullets. Shooting cast bullets fast, with the attendant noise, recoil and barrel wear, for me, is not my cup of tea.

Didn't Col. Harrison shoot cast fast with paper patches, 40 years ago?

Not that I have any issue shooting low velocity stuff. I actually enjoy it very much. But I am not content with that. I want to be able to say I know how to shoot cast at HV, and since I read what LMG wrote and gave it a try.........I can, and have, and the range officers where I shoot have spotted for me while I did it, and shot the rifles. I'm locally famous because of this. There's always a crowd that gathers round when I'm stacking groups with lead at jacketed velocities. It's cool! It's fun! It's repeatable! and its easy to do!

Now, I'm just a gunsmith and a deer hunter, but sometimes I wonder what would happen if a real CBA competitor applied trained shooting techniques to this with an eye on accuracy. Think he might be able to do better than me with my COWW alloy? Better still, if I'm shooting 1.5MOA at 2700FPS, I wonder how I would fare in CBA competition at normal velocities? (I would actually enjoy that immensely, even when I got my clock cleaned. LOL!)

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RicinYakima posted this 09 January 2016

LMG, Issue means as issued for a standard infantryman, so it appears to be more heavily weighted to the shooter abilities side of the equation rather than the ammo making part. Modified Iron is fun because you can “play” with bedding, trigger work, change sights. This is where most new guys begin because there are thousands of sporterized mil-sup rifles and it is cheap to begin shooting. With double aperture sights, ammo making takes on a bigger role in performance. Modified Scope is the most competitive, as some many people want to use a scope (6X limit) as it is better for them. The ability to make ammo for that rifle is at the peak, as sighting errors are so small. IMHO, Ric

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Larry Gibson posted this 09 January 2016

Is there some reason that you don't shoot cast bullets in the 300 yard matches, with both your 14 twist 308 and your 03? I'm sure that they could note in the match results, that you shot cast bullets. It might even give the other guys a incentive to shoot cast, also.   Frank No real reason that I don't shoot cast in the '03 match rifle other than I have about 3,000 M72 bullets for it....

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Larry Gibson posted this 09 January 2016

Ric

I can shoot all of those classes with several rifles. I probably will zero in on the modified iron (M1903A1 NM Type II) or the Modified Scope classes (the M1903A1 NM or a VZ24 8x57 with a Leupold 6X) because, as you note, that's the easiest to start out with. I will then probably move toward the “issue” class for which I have several milsrps for use. Thanks for the quick response and, who knows, I may attend a match up your way as I used to shoot at Paul Bunyon all the time. I have even shot cast bullets on the range their in Yakima come to think of it. We did a test of Little Big Horn battle style rifles and revolvers there for an Army study of the battle. Objective was to see if the soldiers were really “out gunned” because of the M1873 TD and Colt SAAs they had (they weren't). Hope to shoot with you someday.

LMG

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frnkeore posted this 09 January 2016

"Looks like there's CBA matches being held in Phoenix so that sounds good to me.

LMG"

I would suggest that you take either your 14 or 16 twist rifle and shoot in the Heavy Class. I think we would like to see those rifles compete, the most. We all have Milsurp's but, not rifles like that, shooting in the 2700 fps+ area. It could also prove out your “linear Dispersion” as most CBA matches, shoot 100 & 200 yards in both score and 5 & 10 shot groups.

Also, if you show those F class shooters how accurate the HV cast can shoot, I think you'd have some converts. They are WAY cheaper than those match jacketed bullets.

I'm not sure that I agree about the difficuty of swaping a scope for irons, I do it at least 6 times in my 9 day shoot in WA.

As a help, you just need to mark down the sight settings for both the scope and the iron sights. They will repeat better than 1 MOA when swaped back and forth. Not much re-sightig, the day to day conditions can change the sighting that much w/o taking the cope off in my LV stuff and HV should change less, I would think.

Frank

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frnkeore posted this 09 January 2016

"Frank No real reason that I don't shoot cast in the '03 match rifle other than I have about 3,000 M72 bullets for it.... However, I will most likely do some CBA shoots with it over in Phoenix (hopefully). I already have very good 314299 and 311466 loads for it. From the scores posed in CBA matches I should do alright with it.”

I've read that the M72, isn't all that accurate. Match shooters gave up using it long ago. It's a nice looking bullet but, I believe the jackets where not that good.

What RPM will you be shooting? Will you be trying to “push it up"? That 311466, “pushes up” very well, doesn't it?

Frank

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Larry Gibson posted this 09 January 2016

frnkeore wrote: "I've read that the M72, isn't all that accurate. Match shooters gave up using it long ago. It's a nice looking bullet but, I believe the jackets where not that good."The lot of M72/M118 (same bullet) I have holds 1 1/4 - 1 1/2 moa at 2640 fps out of that rifle with 4064, 4895 and Varget which is exactly what it was supposed to do.  I'm kind of nostalgic in my old age and have a bunch of A, B and C old 5V targets.  I built the rifle to shoot M72 bullets on those targets, especially the C target at 800, 900 and 1000 yards.  Even on the NMC Decimal high power targets I can shoot High Master level scores with that rifle.  It's nice to do that but, you're right, the rifle is not competitive with that bullet.  Frankly (no pun intended) the rifle is not even competitive in high power matches with 168, 175 and 180 gr MKs even though they all shoot at or less than 1 moa.  those bullets do have much more uniform jackets.  To be competitive in NRA high power matches with a Match Rifle it has to be 1/2 moa capable.  In many matches these days dropping one point and or having a low X count loses.  Thus I just shoot that rifle for fun.  Same with cast; we know not everyone who shoots cast bullets expects CBA National record accuracy.  Most often less accuracy is very acceptable, especially where fun shooting is done.  Many targets do not require the utmost in precise accuracy, the 5V targets being such.   

What RPM will you be shooting? Will you be trying to “push it up"? That 311466, “pushes up” very well, doesn't it? Since I plan to be shooting CBA military matches with it over at Phoenix where I see by their match scores they only shoot 100 and 200 yards I expect I'll be using the accuracy load that is under the RPM threshold with both the 311466 and the 314299.  Both of those loads will hold 10 ring on the MR-31 and MR-52 targets if I do my part.  Yes the 311466 “pushes up” very well indeed.  Before the advent of the 30 XCB the 311466 was the most accurate HV cast bullet I found.  I do plan on thoroughly testing the 30 XCB bullet though.  I've not done that yet in the match '03.  Of course I will use the most accurate bullet/load for CBA matches regardless of the velocity.  For the VZ24 8x57 I plan on using the 323471.  LMG

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Larry Gibson posted this 10 January 2016

Had a good day at the local prone match but with colder weather (at least for here) the turn out was low with only 8 shooters this morning.  Shot my usual High Master scores.  I've come to learn as most eventually do that age does indeed catch up to us as the target would fuzz up intermittently, especially during the 3rd relay.   I still managed a 196, 197 and 198 which was still satisfying.   After the local match I shot a 20 shot test string at 100 yards with my 30x60.  I have pretty much settled on a “standard load” but previous testing was in 90 - 100+ degree heat.  The barrel heats quick and does not cool in that kind of heat during 10 shot test strings shot within match time limits.  Thus with the 53 degrees today I wanted to see how the 30x60 with the standard load that runs 2890 - 2910 fps would fair.  Accuracy for that standard load has been averaging right around 1.4 - 1.6 moa with 10 shot groups.   As we see I shot a 20 shot group with no additional foulers from a clean barrel.  The first shot (fouler) is the high shot out of the group at 110.  The other 19 shots Went to group.  Even with the lower temperature the barrel still heated up giving a mirage problem.  The shot out at 2 o'clock is the 19th shot and the wind was 0 so the mirage was fairly heavy.  Total 20 shot group size including the fouler was 1.607".  The 19 shots excluding the fouler, went into 1.250"    While this is not 4 five shot groups it is a 20 shot group.  I've found the 10 and particularly 20 shots for score or group are more difficult if fired under match time limits than 5 shot groups.  With 5 shot groups the barrel does generally cool some if not completely between strings.  This brings up the question, in my mind anyway, if we are trying to decipher “flyers in 5 shot groups are they really flyers?  Could it be they are really within the actual cone of fire of a particular load and not “flyers” as such?  I know that 3 shots of the 19 shot group are actually “calls” with the shot going where I called it (all on the edge of the group).  As near as I can measure the majority of shots (15) went into that ragged hole and would be a core group at .75".    At 2900 fps the RPM with the 16” twist barrel is 130,500 demonstrating that by controlling the RPM and using a correctly designed bullet along with other things it's not too difficult to get very good accuracy at high velocity.  The 30 XCB bullets used were visually and then weight sorted.  The bullets in this test weighed 158 - 158.5 gr naked.  They were cast of #2 alloy and WQ'd.   LMG     

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frnkeore posted this 11 January 2016

Excellent, Larry. So, we can expect scores of 195 (X?) @ 100 when you go down to Phoenix? The 10 ring is 3/4", the X is only a dot. The match should be next month.

You can fire as many fouler as you like, so make sure it's well fouled before you start. I can get 3 fouler/sighters off, breech seating before starting.

I checked the Phoenix scores and there are no Mil shooters but, all of Heavy Class shoot 308 Winchesters so, you should be in great company with any of your HV rifles. Frank

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Larry Gibson posted this 11 January 2016

I might do some more accuracy load development for my M70 Match rifle and give the commercial rifle matches a try.  However, Phoenix has military rifle matches scheduled for Feb, Apr, Jun, Aug and Oct.     I'll be warning up my M1903A1 NM Type II for iron modified and either the VZ24 8x57 or the Finn M39 7.62x54R for modified scope.  I might even consider my Russian M911/30 sniper.........decisions.....decisions......   LMG

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frnkeore posted this 11 January 2016

You'll shoot anything but the Heavy class?

I just don't understand :(

Frank

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Larry Gibson posted this 11 January 2016

<user=3132>frnkeore wrote: You'll shoot anything but the Heavy class? I just don't understand Frank I've been known  to shoot some things a little heavier........   LMG

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frnkeore posted this 11 January 2016

That's nothing! I shot a 105mm gun from a M60 tank when at Ft Hood. Very accurate at 1 mile. Frank

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Larry Gibson posted this 11 January 2016

Dang Frank, we went to two different schools together!  Here's me shooting the same at Gowen Field in Idaho.  Also shot them at the Donna Anna ranges north of Fort Bliss.  That was a blast for sure! LMG

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billglaze posted this 11 January 2016

Many years ago, I saw a 10” group shot by the 75mm tube of a M3 at 1000 yds. Impressive--presumably factory loads. It was on an NRA 1000 yd. target; impossible to get an X count; the entire10 ring was nothing but a large hole. I imagine today's 122mm smooth bores with PGM would do as well--probably better. I guess.

Bill

In theory, there's no difference between theory and practice. In practice, there is. My fate is not entirely in Gods hands, if I have a weapon in mine.

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Larry Gibson posted this 11 January 2016

Got out today to conduct the 300 yard bullet recovery test. I used soppy wet newsprint that started out 18” thick when dry but expanded to 26” when wet.  I put an 11 x 8.5 target on front of the wetpack with a 1” paster for an aiming point.  Set up at the bench I wasn't really trying for accuracy but it kind of came out that way.  I didn't want any of the bullets to hit another in the wetpack.  I also was seeking 5 recovered bullets.    

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Larry Gibson posted this 11 January 2016

As it was 3 of the bullets (1, 3 and 4) clustered close together.  On the 5th shot I saw the dirt kick up in the berm out to the left so I knew that shot had been lost.  I adjusted the Leupold target 6.5x20 3/4 moa right and up.  The 6th shot hit the paster, close enough for government work......   For those who like 5 shot groups those 5 shots went into 2.119” at 300 yards with 2900 fps cast bullets.  That figures out to .7 moa.  I can't complain about that.......

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frnkeore posted this 11 January 2016

That 03A3 shoots pretty good

Frank

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Larry Gibson posted this 11 January 2016

As I dug into the wetpack peeling back the newspapers one or two and a time I found the “wound channels to be fairly destructive.  Keeping in mind these XCBs were WQ'd #2 alloy and the impact velocity was 1850 - 1900 fps I was pleasantly pleased.  We see here the results 6” into the wetpack.    

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Larry Gibson posted this 11 January 2016

Three of the XCBs shed their GCs in the wetpack.  I recovered 2 but did not find the 3rd. The recovered separated GCs; one at 17” and one at 19".    The first bullet (#6) was recovered at 20” and it had it's GC.  The second bullet (#2) was recovered at 21” and it also retained it's GC.  Of the three bullets that clustered together (#s 1, 3 and 4) all lost their GCs and two of them penetrated the farthest at 22 and 23". It did not appear that any of the 3 XCBs in that cluster hit another bullet.  Here we see the recovered bullets.   The bullets weighed 163.5 - 164 gr, fully dressed,  before firing.  The recovered weights are (left to right); 140.7 gr, 149.5 gr, 148.5 gr, 145.5 and 152.7 gr. 

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Larry Gibson posted this 11 January 2016

Inspecting the lands and grooves we see evidence of several things occurring during the internal ballistics.  Let us reiterate these bullets were pushed to 2900 fps with a pressure of 50,000 psi.   Here we see an example of some gas cutting on the edge of the rear drive band in front of the GC of the bullet.    

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Larry Gibson posted this 11 January 2016

Here we se gas cutting on another bullet and the chipping of the edges of the drive bands I've seen this chipping numerous times in higher antimony content alloys, especially with linotype.  I'm not surprised to see some evidence here considering the psi used to push the bullets to 2900 fps.

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Larry Gibson posted this 11 January 2016

Another noted occurrence shown in the above photo and the one here is how the GC shank was swaged out to fit the inside confines of the GC.  The photo here also shows how the base was swaged smooth and slightly dished in from the psi.  That is and excellent example of how even hardened #2 alloy can be swaged and the bullet sets back. Another thing to note is the total absence of “skidding” of the bullet over the lands.  With the well designed and properly fitting XCB bullet there is none exhibited here or in any of the recovered bullets.  Not saying it never happens but you'd think at 2900 fps at 50,000 psi there might be a little indication?     

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Larry Gibson posted this 12 January 2016

Additionally it is an example of how well the XCB fits.  Also note the amount of bearing surface which is essential at these higher velocities and may be what's preventing any “skidding” from happening.    Now to the really mind boggling thing discovered here. The bullets were .310 when loaded.  They were fired through a measured and extremely uniform bore of .3077 x .3003.  I expected the diameter of the recovered bullets to be around .308.  I was astounded to find the five recovered bullets diameters measured .303 - .306!  No, the case neck tension was not sizing them down.....I checked that first.  I am befuddled by that but am researching and cogitating on it......any ideas?   LMG       

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goodsteel posted this 12 January 2016

No idea whatsoever. This is fresh new data. My best guess is that hydraulic pressure from the lube sized those bullets down in the barrel, but .005 is an astounding amount. I can't imagine.

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RicinYakima posted this 12 January 2016

I would submit for your consideration that the bullet is in a plastic state upon exit from the barrel. For some distance it is still accelerating until it begins slowing from air resistance. Is there enough supersonic pressure wave acting upon the sides to compress the form, longer and narrower, until it solidifies?

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goodsteel posted this 12 January 2016

RicinYakima wrote: I would submit for your consideration that the bullet is in a plastic state upon exit from the barrel. For some distance it is still accelerating until it begins slowing from air resistance. Is there enough supersonic pressure wave acting upon the sides to compress the form, longer and narrower, until it solidifies? Hard question there. Hard to test, and hard to prove, even if we had access to a high speed video camera. I contacted a friend today who has one of the 14 twist XCB rifles I built (Glenn Larson of White Label Lubes). I described what had been observed here, and also my plans to build a sawdust bullet catcher. He was intrigued by it, and I asked if it were possible to set up on his property one day and shoot a bunch of bullets above and below the RPMTH for observation.  I told him I would bring powder, bullets, sawdust, everything, if we could use his reloading press, rifle, and range. He said it would be a very interesting to test this with several alloys and several of his lubes like 2500, 2700, and the two commercial lubes, just to see what happens.  I still need to lay hands on a boatload of sawdust, but there's a big wood mill a couple towns over that might be willing to drop a bucket load of sawdust in the back of my truck. We'll see what happens. 

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John Alexander posted this 12 January 2016

In Post #73 LMG said:

"This brings up the question, in my mind anyway, if we are trying to decipher “flyers in 5 shot groups are they really flyers?  Could it be they are really within the actual cone of fire of a particular load and not “flyers” as such? “

Absolutely!  That is exactly what almost all fliers in 5-shot groups are -- just Mother Nature at work. Excellent statement.   Anybody that doubts that is what is happening should get out Fouling Shot #213 and stare at Larry Landercasper's sub half minute of angle 25-shot group composed of five 5-shot groups in my article on fliers.  All five of the individual 5-shot groups have “fliers” and a couple of them are extreme.  But when the five groups are put together into one 25-shot group all the fliers disappear into what LMG calls the cone of fire.  If after looking at that group for awhile you still can't see that most fires in 5-shot groups aren't because there was something wrong with that bullet.  Look at it longer until the light comes on. It will save you a lot of heart burn as you shoot 5-shot groups,

John

   

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OU812 posted this 12 January 2016

LMG wrote:    Now to the really mind boggling thing discovered here. The bullets were .310 when loaded.  They were fired through a measured and extremely uniform bore of .3077 x .3003.  I expected the diameter of the recovered bullets to be around .308.  I was astounded to find the five recovered bullets diameters measured .303 - .306!  No, the case neck tension was not sizing them down.....I checked that first.  I am befuddled by that but am researching and cogitating on it......any ideas?   LMG  

Maybe bullets were sqeezed down or sized down while entering wet newspaper?

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goodsteel posted this 12 January 2016

<user=8191>OU812 wrote: <user=7879>LMG wrote:    Now to the really mind boggling thing discovered here. The bullets were .310 when loaded.  They were fired through a measured and extremely uniform bore of .3077 x .3003.  I expected the diameter of the recovered bullets to be around .308.  I was astounded to find the five recovered bullets diameters measured .303 - .306!  No, the case neck tension was not sizing them down.....I checked that first.  I am befuddled by that but am researching and cogitating on it......any ideas?   LMG   Maybe bullets were sqeezed down or sized down while entering wet newspaper? Doubt it very much. Typicly, this medium is used to demonstrate expansion.  John, working with LMG on the XCB project has been educational to say the least, and he has harped on ten shot groups the entire time. LMG once told me that it is statistically impossible to judge a rifle's cone of fire on less than 7 shots, but I have been fooled by that as well. Seems to me that it's really hard to get a “lucky cluster” with ten shots, but  15 gives a veritable certainty of true cone of fire.  Just to help give a point of comparison to the pictures that LMG posted, here is the same bullet that was pushed through a sizing die I made from a piece of rifle barrel. It simply engraves the bullet with rifling under low pressure from the press. I was just finding it interesting to compare the bearing surface to the ones he shot at HV and recovered today. Notice that the amount of bearing surface is virtualy identical, indicating that the ogive did not “bump up” much at all:

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joeb33050 posted this 12 January 2016

LMG wrote:  The 200 yard group is 4.25” with a 2.5” cluster.  Essentially linear expansion of the group size from 50 yards to 200 yards. LMG Larry, you mention this on the 1st page, ...and in non-linear group expansion as range increases...and ...the non linear dispersion of the group size as range increases.

The relationship between group size and range is not linear. 20-0 yard groups are not twice as large as 100 yard groups, in CBA NM results.

7.15.7 HOW MUCH DOES GROUP SIZE CHANGE AS RANGE CHANGES?   5 shot 100 yard groups are .45 times as large as 5 shot 200 yard groups. 5 shot 200 yard groups are 2.2 times as large as 5 shot 100 yard groups. 10 shot 100 yard groups are .43 times as large as 10 shot 200 yard groups.   10 shot 200 yard groups are 2.35 times as large as 10 shot 100 yard groups.   On average See “ACCURACY 100 YARD VS 200 YARD”, in the excel workbooks. This is primarily because wind drift varies as the square of the distance. On calm days, more directly proportional to distance.

This is the seed leading to the conclusion that shooters don't do a very good job holding off for wind, with attendant arithmetic. Hi Gary! joe b.

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Larry Gibson posted this 12 January 2016

joeb   Certainly appreciate your work on that spreadsheet. It does provide useful information.  However it does not give an accurate picture of group linear dispersion as the range increases for an individual shooter. Using the average group sizes for multiple shooters does not give a direct correlation of linear group dispersion by one shooter using the same rifle with the same loads at 100 and 200 yards.

  Let's look at the CBA National Match results fired at Raton last September 12-13.  Let's also keep in mind that no one is saying linear group dispersion is exactly 2 times as much from 100 to 200 yards.  As you note there are other variables to be considered as the range increases, primarily the wind.   There were 9 shooters that finished the 10 shot matches at 100 and 200 yards in the Heavy Rifle classification.  I use that because that would be the classification my 30x60 XCB rifle would fall into.  Here are the aggregate 10 shot group sizes at 100 and 200 yards by each shooter:

100 yds     200 yds

0.847         2.988 1.131         2.554 1.137         2.644 1.433         2.106 0.956        3.703 1.044        3.834 1.105        3.992 1.823        3.651

Thus we see by comparing the results of each shooter with the same rifle and load in one instance the linear dispersion at 200 yards was less than 2 times (1.47)the 100 yard group dispersion.  In one case the linear dispersion was exactly 2 times the 100 yard group size.  In the remaining 7 instances the 200 yard group size was more than 2 times the 100 yard group size (2.26 to 3.6). 

It appears from the listed equipment and velocities that the top shooters (3 or 4 of the 9) were better at judging the wind than the others as their 100 and 200 yard groups remained close to linear dispersion.  As you mention in your treatise it is the wind that is a problem with many at longer ranges.  Of course the wind only adds to the dispersion as a separate component and is really not a part of it from a ballistic perspective.    Then even when we take the average of the 100 yards groups (1.154") and compare it to the average linear dispersion of the 200 yard groups (3.184") we find the 200 yard groups to be 2.75 times larger than the 100 yard groups.  Thus we find that at 2900 fps with the XCB bullet in the 30x60 XCB cartridge I am “competitive” in groups sizes with the competitors at the Nationals.  That is always good to know.   LMG  

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joeb33050 posted this 12 January 2016

LMG wrote: joeb   Certainly appreciate your work on that spreadsheet. It does provide useful information.  However it does not give an accurate picture of group linear dispersion as the range increases for an individual shooter. Using the average group sizes for multiple shooters does not give a direct correlation of linear group dispersion by one shooter using the same rifle with the same loads at 100 and 200 yards.

  Let's look at the CBA National Match results fired at Raton last September 12-13.  Let's also keep in mind that no one is saying linear group dispersion is exactly 2 times as much from 100 to 200 yards.  As you note there are other variables to be considered as the range increases, primarily the wind.   There were 9 shooters that finished the 10 shot matches at 100 and 200 yards in the Heavy Rifle classification.  I use that because that would be the classification my 30x60 XCB rifle would fall into.  Here are the aggregate 10 shot group sizes at 100 and 200 yards by each shooter:

100 yds     200 yds

0.847         2.988 1.131         2.554 1.137         2.644 1.433         2.106 0.956        3.703 1.044        3.834 1.105        3.992 1.823        3.651

Thus we see by comparing the results of each shooter with the same rifle and load in one instance the linear dispersion at 200 yards was less than 2 times (1.47)the 100 yard group dispersion.  In one case the linear dispersion was exactly 2 times the 100 yard group size.  In the remaining 7 instances the 200 yard group size was more than 2 times the 100 yard group size (2.26 to 3.6). 

It appears from the listed equipment and velocities that the top shooters (3 or 4 of the 9) were better at judging the wind than the others as their 100 and 200 yard groups remained close to linear dispersion.  As you mention in your treatise it is the wind that is a problem with many at longer ranges.  Of course the wind only adds to the dispersion as a separate component and is really not a part of it from a ballistic perspective.    Then even when we take the average of the 100 yards groups (1.154") and compare it to the average linear dispersion of the 200 yard groups (3.184") we find the 200 yard groups to be 2.75 times larger than the 100 yard groups.  Thus we find that at 2900 fps with the XCB bullet in the 30x60 XCB cartridge I am “competitive” in groups sizes with the competitors at the Nationals.  That is always good to know.   LMG  

You know Larry, I know what each of your words means, I know what some of your sentences mean, but I have no idea what you're talking about. The sample size you use is 8, that's 8, and with a sample size of 8 you know just about nothing.

Group size is not proportional to range, relative group size is greater than proportional. I suspect that the wind is the cause, it's the only effect that's not linear. This has nothing to do with any rpm threshold. Perhaps Gary could explain it to me.

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Larry Gibson posted this 12 January 2016

You're right joeb, I left one out. the group sizes for that are:

0.910” at 100 yards and 3.187” at 200 yards.

The 200 yard group size is 3.5 times larger than the 100 yard group. However that dispersion rate is still within the averages in my post above. Thanks for catching the omission.

Yah know joeb, I may not know nothing about nothing but the match results speak for themselves. It's unfortunate you have no idea what I am talking about. Is there some way to make it clearer?

LMG

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John Alexander posted this 12 January 2016

goodsteel wrote: ” LMG once told me that it is statistically impossible to judge a rifle's cone of fire on less than 7 shots, but I have been fooled by that as well."

Yes a 7-shot group will fool you as will a 10-shot group sometimes --  but not as often. With all due respect, I believe LMG got what a 7 shot group is notable for mixed up with finding a zero (where the cone of fire is centered.) When finding a zero, the the more shots in the group the better.  Although like most things in nature it is subject to the law of diminishing returns e.g. a 6-shot group is a LOT better for finding a zero than a 3-shot group whereas a 40-shot group is only A LITTLE better than a 20-shot group. But there is no break point in the curve at seven.     Seven-shot groups get mentioned as special because it is the group size that statistically gives the most information from a given number of total shots fired -- if the human factors are ignored. Though again, 7 isn't magical and 5-shot and 10- shot groups are almost as efficient given the same number of total shots fired.     Good luck with your oiled sawdust bullet catcher.  Mine of loose wool was a failure and I hope to also build one filled with oiled sawdust.  Your and LMG's results so far are interesting.  Keep up the good work.   John

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frnkeore posted this 12 January 2016

Ok Larry, This is another area that I always disagreed with you on and it's the reason I put “quotes” on the term when I talk about it with you.

You harp about this all the time on the boolit forum and try to use it to discredit people, over there. If they do well with a 10 twist, you say “did you test it for linear dispersion” which, of course they can't. Not only that but, you and the crew, post scores of groups, shot at 100 and hardly any at 200 but, even so, you talk a “linear” all the time. I have to say as JoeB does, “where's the data"?

As a match shooter, I live in the real world regarding this issue and I see the results on paper very month.

You then conveniently “forget” to add in the one of the largest veriables and find that what “you” added up was 2.75, not what you say it should be. Rather than indicate you your “theory” might be subject, you talk about how your rifle will be competitive but, you say that you won't shoot it in matches, why's that? Especially since it remains to be seen if you'll ever shoot in a match with ANYTHING.

If you will study what the wind actually will do to a bullet between 100 and 200 yards, I think you would give this up. Even if you could do your testing in a tunnel, it's not the real world and we all shoot in the REAL world, not some dream world.

Not to mention (I like that term :) ) that it matters NOT in competition, the winner is the Winner, no matter the ratio of the group sizes. So, maybe you should work on changing the rules so, that if a match is won and the group doesn't fall into your theory, the entrant is disqualified?

Frank

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John Alexander posted this 12 January 2016

We have differences of opinion or opinions here and that is what a forum is good for but a little edge in the “tone' is creeping into the posts.  I urge you all to read your posts as if they were being sent to you and modify as needed.

If we want to make progress towards what is true and what isn't, and I think we all do, we have to define our terms and and carefully state exactly what we are claiming. Then state our evidence clearly so we aren't talking past one another.

I regret that my two latest posts are off the main topic although I'm not exactly sure what the main topic is.  Please disregard my contributions to the confusion.

It seems to me that this thread has the potential to be a great discussion or something that will be deleted.

Thanks for you consideration.

John

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frnkeore posted this 12 January 2016

John, Your on topic. The topic being The RPM Threshold. In his threshold theory, LMG, claims that if you shoot a group, above his “threshold” it will not be “linear” and therefore, proves his theory. But, when there is proof that it's been done, he just says that, that person “push” His “threshold” up, rather than saying that with good loading technics, equipment and materials, there may be no limits to what can be done with cast bullets.

Frank

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Larry Gibson posted this 12 January 2016

Well obviously Frank you have proven you're not here for the party but to argue. I won't argue with you but will note: I had a long response written out but just decided to delete it.

No I'm not going to let you goad me into another long discussion as all you want is an argument. Your post besides being non-factual,is impolite to say the least.

You have a nice day Frank.

LMG

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frnkeore posted this 12 January 2016

Let me add something related to this discusstion:

Does anyone know why a bullet needs to spin, to begin with, other than it makes a projectile more accurate?

Frank

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Larry Gibson posted this 12 January 2016

frnkeore wrote: Let me add something related to this discusstion:

Does anyone know why a bullet needs to spin, to begin with, other than it makes a projectile more accurate?

Frank
Because bullets have their center of pressure located in front of their center of mass.  That is statistically unstable configuration.  In order for the statistically unstable bullet to maintain a point forward flight there must be adequate spin to achieve and maintain gyroscopic stability.   That's not my theory Frank.  You'll find it right out of books on ballistics such as Bryan Litz's Applied Ballistics For Long-Range Shooting.    LMG   Might add that there are lots of bullets that are gyroscopically stable that are not very accurate; milsurp bullets, poorly cast bullets and bullets over the RPM Threshold.

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joeb33050 posted this 12 January 2016

frnkeore wrote: Let me add something related to this discusstion:

Does anyone know why a bullet needs to spin, to begin with, other than it makes a projectile more accurate?

Frank If you go to the second page, page 289, about a third of the way down, starting with "It was in 1746...

This suggests that a rifled barrel is better than a smoothbore, because a smoothbore can/will introduce a randomy twist.

That's one answer to the why?

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joeb33050 posted this 12 January 2016

frnkeore wrote: Let me add something related to this discusstion:

Does anyone know why a bullet needs to spin, to begin with, other than it makes a projectile more accurate?

FrankOr for those of us who is familiar with the dreaded cosine...

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Larry Gibson posted this 12 January 2016

In addition to the test I posted in this thread (posts 36, 38 and 39) which were also posted several times several years ago on the “other forum” I am posting this test to help clarify the concept of “linear and non-linear” group dispersion as the range increases here is a test I posted on “the other forum” about a year ago conducted with the same 30x60 XCB rifle.   Linear testing; 100, 200 and 300 yards   As I said in my last post on the results from the 30x60 using the 16” twist rifle Dawn, the next step would be to conduct a longer range test of the 49.5 gr LeveRevolution load to test for linear group dispersion. I conducted that test this morning at 200 and 300 yards. The load was the same; 49.5 gr LvR with a Dacron filler (1/3 gr). The bullet was the 30 XCB cast of linotype and WQ'd. Velocity runs right at 3000 fps with the linotype bullet sized at .310 and lubed with 2500+. Looking at the 100 yard groups of 49 and 49.5 gr LvR I shot the other day and posted in the last report we see basically 1.4 - 1.5 moa between the two of them.  

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Larry Gibson posted this 12 January 2016

2nd 100 yard group.

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Larry Gibson posted this 12 January 2016

I then put a target at 200 yards and measured the wind.......it was still coming out of 1 - 2 o'clock but had picked up running from 7 - 10 and gusting to 12 mph. It also would just die momentarily. I shot the 10 shots trying to gues when the wind was consistent but with no real wind indicators other than the feel of it at the bench I didn't do to well. That nice 5 shot group to the right is the result of the wind dying just as I pulled the trigger! None the less the over all group is right at 3” for again, 1.5 moa. There is an eleventh shot in there for you bean counters; I took 3 foulers with me and fired 2 before the test. I decided to shoot the last fouler into the 200 yard group. It is the high left shot of that five shot group on the right from when the wind died.

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Larry Gibson posted this 12 January 2016

A Target was then put up at 300 yards and another 10 shot group shot on it.  As we see the group size is right at 4.5”.  That is well within the linear expansion for 100, 200 and 300 yards.

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Larry Gibson posted this 12 January 2016

This test demonstrated the linear group expansion/dispersion is consistent at 1.5 moa for 100, 200 and 300 yards. That is exactly what we were looking for. This is an excellent load and will probably be my go to HV load for Dawn. I will be further testing this load at 400 - 600 yards in the near future. However, I have one other Powder to test with the linotype 30 XCBs. The testing continues but the RPM Threshold is well proven. What is also well proven is how to shoot real HV with cast bullets accurately if that is your goal.   To further explain let me post a couple graphs showong the difference between linear and non-linear group dispersion between 100 and 200 yards.  The smallest and largest groups for each comes from the 311291 test conducted at the beginning of this thread.   As we all know the “average” group size is just that....an average.  The same load given four 5 shot groups or two ten shot groups which are shot with the same load give us the smallest group and the largest group I.e. an a spread of “accuracy” to which any group fired with that same load and rifle can be expected to be within.  Thus with a ten shot group fired at 100 yards that group may fall at the large end of the range.  The next group shot at 200 yards may be at the lower end of that range.  If we have a load that shoots consistently between 1.0 and 1.5” the we could have a 1.5” group at 100 yards and a 2” group at 200 yards.  Not an “exact” expansion of Xs 2 but still with in the expected linear expansion accuracy range of the load/rifle.    Here is a graph demonstrating both linear and non-linear expansion.  The linear expansion occurred with the load under the RPM Threshold at 1900 fps +/-.  The outside dotted lines are the non-linear expansion of the load over the RPM Threshold.  On each side you have the linear expansion line of the largest expected shot group (lines 1L and 1R).  On the inside we have the expansion lines of the expected smallest group (2L and 2R).  On each outside the dotted lines represent the non-linear expansion of the load over the RPM Threshold.    

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Larry Gibson posted this 12 January 2016

John Alexander wrote: goodsteel wrote: ” LMG once told me that it is statistically impossible to judge a rifle's cone of fire on less than 7 shots, but I have been fooled by that as well."

Yes a 7-shot group will fool you as will a 10-shot group sometimes --  but not as often. With all due respect, I believe LMG got what a 7 shot group is notable for mixed up with finding a zero (where the cone of fire is centered.) When finding a zero, the the more shots in the group the better.  Although like most things in nature it is subject to the law of diminishing returns e.g. a 6-shot group is a LOT better for finding a zero than a 3-shot group whereas a 40-shot group is only A LITTLE better than a 20-shot group. But there is no break point in the curve at seven.     Seven-shot groups get mentioned as special because it is the group size that statistically gives the most information from a given number of total shots fired -- if the human factors are ignored. Though again, 7 isn't magical and 5-shot and 10- shot groups are almost as efficient given the same number of total shots fired.    

John
John   I consider both you and goodsteel absolutely correct.  The less than 7 shots I was referring to is what many ballisticians refer to.  We see it mentioned in a couple loading manuals.  Actually 10 shots is the industry standard as evidenced by it's use by SAAMI.  It gives a reasonable surety of the quality of the load either and to ballistics or as to zero.  In testing I use a minimal 10 shot group and then like to use 2 or 3 additional 10 shot groups as confirmation.   Back in the day when I was instructing NMC marksmanship I required a 20 shot group to establish an adequate cone of fire at each range.  Once that was established the sights could be used to bring the center of the group to zero.  I also used at least a 20 shot group on the 25M zero range for military shooters.  The “zero in 9 rounds with three 3 shot groups” was found woefully lacking.  When the troop could literally shoot a ragged hole out of the middle of the 25 yard zero target the solder was zeroed, had confidence and always then did well on the KD and qual ranges.      Wish I had a location to build a trap.  Either to hold sawdust or ground up tires.  I always thought with sawdust a long trough made of wood would do.  The bullet could be located with a metal detector and then easily recovered with the trough then ready for the next shot.  Just my idea......   LMG

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John Alexander posted this 13 January 2016

LMG,

             I would like to make sure I understand your term linear group expansion.&nbsp; Since linear refers to a straight line it seems that the term means that the group size is proportional to the distance.&nbsp; Your example above of 1.5. 3. and 4.5 inch groups at 100, 200, and 300 yards would be proportional to distance.&nbsp; If we are in agreement, we can go on.

  I don't doubt that you shot the three groups above but that is a sample of 1 and a sample of one is seldom reliable. I would give good odds that you can't do it again even on the same day or any other day and I would give very high odds that you couldn't do it three times in a row.  The reason I would be generous in offering odds is because others can't do it either as Joe's and your own figures above show. Finding groups that increase in size exactly in proportion to the distance, or linearly, are rare if shot in the open air although they may approach a linear increase in a tunnel or in very good conditions. Do you agree?  

John   

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RicinYakima posted this 13 January 2016

"Wish I had a location to build a trap.  Either to hold sawdust or ground up tires.  I always thought with sawdust a long trough made of wood would do.  The bullet could be located with a metal detector and then easily recovered with the trough then ready for the next shot.  Just my idea....." The wood trap has been done at least since the 1890's, by Dr. Hudson and the Schuetzen guys. Just a thought for your correspondence with Goodsteel: consider building it with glue if you are going to use a medal detector, as screws and nails may upset your search. But I don't know much about metal detectors.

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goodsteel posted this 13 January 2016

Ric, I'm just going to do exactly as you and I discussed. Cardboard dividers are much cheaper than a metal detector, and once you run out of cardboard with holes in it, you know you're within a 16” cube of the bullets right? Digging through 16 cubic inches of oily sawdust isn't a hard job, and a metal detector wouldn't change the necessity to do it. 

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Larry Gibson posted this 13 January 2016

Looks like you guys have given the sawdust bullet trap a lot more thought than I have. I was just thinking about it having seen a picture and small discussion of one many years ago, probably from the sources Ric mentions. Cardboard dividers sounds like a good idea to me.   I had a long length of plastic pipe/culvert of 15 - 20” diameter in mind with slots cut length wise along the top to access the bullet in the oil soaked sawdust.  No glue needed and no screws/nails needed to foil the metal detector. 

LMG

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Larry Gibson posted this 13 January 2016

John Alexander wrote: LMG,

I would like to make sure I understand your term linear group expansion.  Since linear refers to a straight line it seems that the term means that the group size is proportional to the distance.  Your example above of 1.5. 3. and 4.5 inch groups at 100, 200, and 300 yards would be proportional to distance.  If we are in agreement, we can go on.   I don't doubt that you shot the three groups above but that is a sample of 1 and a sample of one is seldom reliable. I would give good odds that you can't do it again even on the same day or any other day and I would give very high odds that you couldn't do it three times in a row.  The reason I would be generous in offering odds is because others can't do it either as Joe's and your own figures above show. Finding groups that increase in size exactly in proportion to the distance, or linearly, are rare if shot in the open air although they may approach a linear increase in a tunnel or in very good conditions. Do you agree?  

John   
John   Your concept of linear group expansion is spot on.  A bit of further explanation.  The term is used in ballistic books and works when discussing small arms cartridge accuracy at longer ranges.  “Linear", while thought of as a straight line, is in this case a derivative of “linear measure” which is a measure of length assumed to be equal in length.  That being in the case used here to represent proportional group expansion at 100, 200 and 300 yards as you state.    I've shown one example here done with the 30x60.  On page 2 of this thread are examples of both linear and non-linear group expansion at 50, 100 and 200 yards.  I have conducted linear testing at those ranges and out to 300 for several years with several different rifles of different twist rates.  I have duplicated the results (both linear and non-linear group dispersion) shown here on demand many times.  As I've mentioned I am going to test 7 ten shot groups at 300 yards of the same load with only the weight of the bullet varying by .1 gr.  I could shoot 100 and 200 yards again also again if you'd like?   The problem with Joe's and my own figures is they are published averages, not the actual group sizes.  Let's say you've a rifle that you shoot 5 ten shot groups and 100 yards; 1, 1.25, 1.5, 1.75 and 2.0".  The average group size is 1.5” but in reality that is not the “accuracy capability” of the rifle and load.  We know because 50% of the time it will shoot better and 50% of the time worse.  What we can say is the accuracy capability of the rifle/load is 1 - 2 moa though and be correct.

Now you know the next time you shoot a ten shot group at 100 yards odds are it will be between 1” and 2” but only a very small chance it will be 1.5"....the average.  So lets say there is no wind or mirage to deal with and you shoot a 2” group at 100 yards and then again a 2” group at 200 yards.  Did the rifle/load all of a sudden get more accurate?  Did the bullets “go to sleep” and were more accurate at 200 yards?  The answer to both questions is....no.  The 100 yard group was within the accuracy capability of the rifle/load as was the 200 yard group.  Both the 100 and 200 yard groups were in the 1 - 2 moa capability of the rifle/load.  The linear dispersion at 200 yards is 2 - 4 moa (twice the dispersion range of 1 - 2 moa at 100 yards) and that 200 yard group of 2” was in that range.    Thus we see the linear 200 yard group dispersion size is not a function of the 100 yard average group size.  It is not even a function of the exact size of a 100 yard group shot during a test.  The 200 yard group does not have to be exactly twice the size of the 100 yard group.  Linear group dispersion is a function of the actual accuracy capability of the rifle/load.  In other words if we expect a group of 1 - 2” at 100 yards we can expect a group of 2 - 4” at 200 yards and 3 - 6” at 300 yards.   LMG    

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frnkeore posted this 13 January 2016

"Now you know the next time you shoot a ten shot group at 100 yards odds are it will be between 1” and 2” but only a very small chance it will be 1.5"....the average. So lets say there is no wind or mirage to deal with and you shoot a 2” group at 100 yards and then again a 2” group at 200 yards. Did the rifle/load all of a sudden get more accurate? Did the bullets “go to sleep” and were more accurate at 200 yards? The answer to both questions is....no. The 100 yard group was within the accuracy capability of the rifle/load as was the 200 yard group. Both the 100 and 200 yard groups were in the 1 - 2 moa capability of the rifle/load. The linear dispersion at 200 yards is 2 - 4 moa (twice the dispersion range of 1 - 2 moa at 100 yards) and that 200 yard group of 2” was in that range.

Thus we see the linear 200 yard group dispersion size is not a function of the 100 yard average group size. It is not even a function of the exact size of a 100 yard group shot during a test. The 200 yard group does not have to be exactly twice the size of the 100 yard group. Linear group dispersion is a function of the actual accuracy capability of the rifle/load. In other words if we expect a group of 1 - 2” at 100 yards we can expect a group of 2 - 4” at 200 yards and 3 - 6” at 300 yards."

Another way of Manipulating the data to suit a theory. By this method, you need to know that info about all the rifles that shot groups in the data in question.

If that data isn't available no one can do the math on it by this method and no one can be right or wrong, not even LMG.

But, in legal terms, a preponderance of the evidence (the collection of groups) is what you have to work with. In the past, LMG has stated that the CBA records are proof of his linear theory but, they are just one exceptional group each and not supported by his lastest theory. Why do I know this? Because we have had conversations, regarding it in the past.

With the info that LMG has supplied, I believe that his 300 yard testing will have to be done posting 3 targets (100, 200 & 300 yd) and shooting them in order by putting one shot on each, 10 different times for the 7, ten shot groups.

Am I right, or are you going to assume that the 100 & 200 yard groups would have been linear?

Frank

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frnkeore posted this 13 January 2016

<user=7879>LMG wrote: <user=3132>frnkeore wrote: Let me add something related to this discusstion: Does anyone know why a bullet needs to spin, to begin with, other than it makes a projectile more accurate? Frank Because bullets have their center of pressure located in front of their center of mass.  That is statistically unstable configuration.  In order for the statistically unstable bullet to maintain a point forward flight there must be adequate spin to achieve and maintain gyroscopic stability.   That's not my theory Frank.  You'll find it right out of books on ballistics such as Bryan Litz's Applied Ballistics For Long-Range Shooting.    LMG   Might add that there are lots of bullets that are gyroscopically stable that are not very accurate; milsurp bullets, poorly cast bullets and bullets over the RPM Threshold. First, there is a difference between Stability and Accuracy. A bullet can be stable and not accurate and also be unstable and accurate, as the pictured target I will post shows. It was shot at 200 yards in a match in Modesto. While the CG & CP can have some effect on the amount of spin a bullet takes to attain stablity, the reason that a bullet needs to spin is that it has to become a gyroscope, to maintain a forward atitude and along with that, it also has to have a flywheel effect to to keep that amount of spin for the distance covered. And the flywheel effect, is the reason that as the diameter becomes larger, the twist rate decreases to maintain bullet stability. To my knowlege, LMG has never said that his 120-140K rpm had anything to do with caliber but, maybe, he thinks that the world is only 30 cal? But, he does shoot jacketed 223. Here is what happens regarding stability and caliber for a 1” long bullet. If a 223 shooter where to use the “threshold” the bullets might tumble and the 45 cal would be way over stablized. <color="#000000"><size="2"><font="Arial"> 1.5 GS @ 2000 fps<color="#000000"><size="2"><font="Arial"> <color="#000000"><size="2"><font="Arial">   .458,  36,000 RPM<color="#000000"><size="2"><font="Arial"> <color="#000000"><size="2"><font="Arial"> .358,  62,900<color="#000000"><size="2"><font="Arial"> <color="#000000"><size="2"><font="Arial"> .338,  77,100<color="#000000"><size="2"><font="Arial"> <color="#000000"><size="2"><font="Arial"> .308,  85,700<color="#000000"><size="2"><font="Arial"> <color="#000000"><size="2"><font="Arial"> .264, 119,000<color="#000000"><size="2"><font="Arial"> <color="#000000"><size="2"><font="Arial"> .224, 170,400<color="#000000"><size="2"><font="Arial"> <color="#000000"><size="2"><font="Arial"> .174, 290,900<color="#000000"><size="2"><font="Arial"> <color="#000000"><size="2"><font="Arial"> Frank<color="#000000"><size="2"><font="Arial"> <color="#000000"><size="2"><font="Arial"> A 1.25 MOA target (6 in .5 MOA), almost all tipped.

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goodsteel posted this 13 January 2016

I've noticed that the RPMTH is lower for larger bullets and higher for smaller bullets. It's still there though, and anybody can go see it for themselves if they feel like loading up and shooting. I'm comfortable with that.

Now, I just called the local paper mill, and after getting passed up the chain a few times, I was talking to the main man himself. I told him about our project, and explained who I am and what I'm trying to do. Turns out, the guy has a choke tube stuck in his shotgun:cool: Long story short, I can go and get a pickup truck full of sawdust any time. All I have to do is call and let him know.

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frnkeore posted this 13 January 2016

"I've noticed that the RPMTH is lower for larger bullets and higher for smaller bullets. It's still there though, and anybody can go see it for themselves if they feel like loading up and shooting. I'm comfortable with that.”

With all do respect, Tim, that is a assumption, right?

Frank

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HuskerP7M8 posted this 14 January 2016

<size=4><font="Times New Roman">When Lapua announced they were opening a 100 M test range in Mesa, Arizona with Meyton Electronic targeting systems at both 50 M and 100 M, I thought it might be possible to gather enough quality data to calculate the ratio for non-linear group growth due to increased distance for RF ammunition.   Over the last several years I've accumulated the statistics for approximately 100 groups and the following screenshot is a 15 group subset for a single rifle. The next 2 screenshots are the actual groups printed out by the Meyton system and they show the extremes for the calculated ratios.   Landy   Max & Min non-linear group growth.  3.62:      1.99:   

“In God we trust; all others must bring data.” “Without data, you're just another person with an opinion.” “If you can't describe what you are doing as a process, you don't know what you're doing.” “It is not enough to do your best, you must know what to do, and then do your best.” W. Edwards Deming (October 14, 1900 - December 20, 1993)

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goodsteel posted this 14 January 2016

frnkeore wrote: "I've noticed that the RPMTH is lower for larger bullets and higher for smaller bullets. It's still there though, and anybody can go see it for themselves if they feel like loading up and shooting. I'm comfortable with that.”

With all do respect, Tim, that is a assumption, right?

Frank Well, it depends on how you define an assumption. There are those who lean on what they read on the internet to form an accurate opinion, based on the assumption that the information is correct, then try desperately hard to argue with people who are basing their conclusions on first hand experience.   My comment above was based on what I have seen in my own rifles, and conversations I have had with clients who also actually shoot HV and formed their opinions on first hand experience (rather than estimated figures and tall tails they read on the internet. You see the difference.) 

Here is what I have seen in rifles that have been thoroughly tested and what I based my statements on: 

22, 6mm and 6.5mm rifles which often blow as high as 150,000 RPM  30 caliber rifles which routinely blow out at 140,000RPM (My own included)  My 35 XCB was built to provide enough case capacity to push up to the RPMTH, and the threshold was found regularly at 133,000RPM. One of my clients has thoroughly tested cast bullets in the 50BMG and has reported that he cannot shoot past 115,000 RPM with any degree of long range accuracy. 

That's what I based my comment on. I see a trend in the data and I recognized it. 

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Ken Campbell Iowa posted this 14 January 2016

regarding bullet catcher/recovery ...

cardboard partitions :::; seems that would work fine for the first shot ( s ) ... but once you pull the cardboards out of the oiled sawdust it would be ... problematic ... pushing thin carboard back into the chips.

how about separate cardboard boxes of chips set on an indexed frame ... 3 inches separation so you could just see how many boxes down the line you need to search into ...

after several shots you might need to tape a copy paper on the box entrance y exit to keep the chips from dribbling out . or if you can find a source of thin boxes just pour a fresh box occasionally .

wonder if harbor freight has a metal detector for $50 ?? my plumber has a cheap looking rig . will find a bolt 2 to 6 feet away .

gee we are getting closer guys ...

ken

EDIT: expletive deleted ... harbor freight has a metal detector for $18... walmart $46 .... anybody wanna buy a job shop that used to make american products ??

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goodsteel posted this 14 January 2016

I don't need a metal detector, but the cardboard box idea is brilliant! I may give that a try.

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John Alexander posted this 14 January 2016

We have at least two conversations going here. Both are interesting but  it is confusing and non productive. I will start a new thread for bullet catchers. Discussing the original topic is hard enough as we have seen without the confusion.

John

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John Alexander posted this 14 January 2016

Husker, This is a check to see if I understand what I think I see in the data you posted. 

By being able to measure the same group at both 50 and 100 yards with the Meyton Electronic gadgets, you can see the actual expansion of a single group from 50 to 100 yards.  This eliminates the complication of considering the natural variation of group sizes from one to another when different groups are measured at the two distances.

This eliminated the need, and hopeless complication, of needing to consider the concept of the expansion of a “cone of fire” as explained by LMG in post #117.  

Further, your data gives very strong evidence that the expansion of groups is not linear since only one group showed an expansion of being less than proportional to distance (i.e. 1.99.) 

Stated another way for high quality 22rf ammo in a very high quality rifle and under the conditions of the test you report and with a bullet rpm of 47K, group expansion is seldom if ever linear.

Do I understand what I see?

John

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Larry Gibson posted this 14 January 2016

Husker Do you know what Lapua's conclusion on the quality of that ammunition was? What I see in those two targets is a definite 2 - 3 flyers in each group. If we look at the core 100 yard group in each example we see the expansion is linear. I doubt that Lapua would find that ammunition acceptable for match shooting the 50/100m competitions. Having considerable small bore competition myself ( used an Anschutz Match rifle) experience myself I can say any serious small bore competitor would not use that ammunition in competition. I know I wouldn't. An excellent example of non linear group dispersion but I would not say it proves All groups fired are non-linear. It only proves there was something wrong with that ammunition. We could say that linear dispersion of the shot group is and has been for a long time an accuracy expectation simply based on the targets we use.  Take the Small bore 50 and 100 yard or NM High Power 600 and 1000 yard targets for example.  The scoring rings are linear in expansion as the range increases.  The NM 600 yard 10 ring is 2 moa.  The 1000 yard 10 ring is 2 moa.  The X rings for both are 1 moa.   So how does that correlate to cast bullet shooting? The targets used in our military matches is the 600 yard match target reduced for use at 100, 200 and 300 yards.  The 10 ring of all three targets is 2 moa based on the use of a 30 caliber bullet (to cut the ring for score with).  In other words the 200 yard 10 ring is twice as large as the 100 yard 10 ring.  The 300 yard 10 ring is 3 times as large as the 100 yards 10 ring.  That is linear expansion.   So lets take a look at the 2015 National scores for Modified Scope.  The top ten shooters average 100 yard score was 192.5.  Their average 200 yard score (on the linear increased in size scoring rings on the 200 yard target) was 187.5.  I agree with joeb that we must factor in a bit of the wind at the longer range. Even not factoring the wind we see the 200 yard scores are .975 % of the 100 yard scores.  If we look at the top 5 shooters, who were probably judging the wind and conditions better, we see they had a 100 yard average of 193.8 and a 200 yard average of 191.  That shows the 200 yard scores were 98.5% of the 100 yard scores.  That is a very good example of linear dispersion of the group sizes.   But there is a problem with making assessments comparing the difference between 100 and 200 yards just based on posted scores or group sizes.  The problem is two fold; we don't know the conditions those scores and groups were shot in and we don't see the “whole picture", i.e. the actual targets and groups.  Here is an example of how we can be led astray and how our computated assessments can give us the wrong answer, especially when just assessing group sizes.    The example is of two shooters competing in Military Modified Rifle. Shooter #1 has a good load, not great but good, and is a consistent shooter.  His posted 100 yard group is 1.25 and his 200 yard group is 2.5” which is linear dispersion.  His aggregate is 1.875.  Shooter #2 is a very good shooter with a very good rifle and a very good load.  His posted 100 yard group is 1.1” and his 200 yard group is 2.9".  That seems to indicate non-linear group expansion.  But is it?  If we can see his group and know what happened we see his 200 yard core group of 9 shots is 2.25” which is linear expansion based on the 100 yard group.  What we don't know is Shooter #2 had a brain fade and pulled one shot out to the left giving him the group size of 2.9".  What we don't know by the posted results is that one shot, the called flyer, skewed the results.  Shooter #2's aggregate is 2” but looking at the actual targets who has the more accurate load and was there linear or non-linear dispersion?   The drawing is just an example and not to scale. LMG

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frnkeore posted this 14 January 2016

Linear expansion of the reduced 600 yard, NRA targets.

MR31-100-10 ring . . . . . . . . . 1.75 MR52-200-10 ring . . . . . . . . . 3.79 = 2.166 MR63-300-10 ring . . . . . . . ... 5.85 = 3.343

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frnkeore posted this 14 January 2016

So Laupa is also suspect because they don't agree with LMG!

Those are just 2 of 15 groups. No others are pictured, just the largest and smallest. Both have “fliers” yet one corresponds to LMG's beliefs. We have no info that there where fliers in any other groups but, I guess he assumes that.

Through out the years, in targets that LMG post (there are many of them) he seem to denote that the one or more shots that don't go into a group are either foulers or called errors, maybe even sight adjustments. When posting things to prove something, you should NOT shoot foulers into a group and if there is a “called” something, the target should be repeated. That's the beauty of Match shooting........ you don't get to do that!

I don't know what to call this but, more fanticy:

"But there is a problem with making assessments comparing the difference between 100 and 200 yards just based on posted scores or group sizes. The problem is two fold; we don't know the conditions those scores and groups were shot in and we don't see the “whole picture", i.e. the actual targets and groups. Here is an example of how we can be led astray and how our computated assessments can give us the wrong answer, especially when just assessing group sizes.

The example is of two shooters competing in Military Modified Rifle. Shooter #1 has a good load, not great but good, and is a consistent shooter. His posted 100 yard group is 1.25 and his 200 yard group is 2.5” which is linear dispersion. His aggregate is 1.875. Shooter #2 is a very good shooter with a very good rifle and a very good load. His posted 100 yard group is 1.1” and his 200 yard group is 2.9". That seems to indicate non-linear group expansion. But is it? If we can see his group and know what happened we see his 200 yard core group of 9 shots is 2.25” which is linear expansion based on the 100 yard group. What we don't know is Shooter #2 had a brain fade and pulled one shot out to the left giving him the group size of 2.9". What we don't know by the posted results is that one shot, the called flyer, skewed the results. Shooter #2's aggregate is 2” but looking at the actual targets who has the more accurate load and was there linear or non-linear dispersion?

The drawing is just an example and not to scale.

LMG

Attached Image:"

Frank

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John Alexander posted this 14 January 2016

LMG said:What I see in those two targets is a definite 2 - 3 flyers in each group. If we look at the core 100 yard group in each example we see the expansion is linear. I doubt that Lapua would find that ammunition acceptable for match shooting the 50/100m competitions. Having considerable small bore competition myself ( used an Anschutz Match rifle) experience myself I can say any serious small bore competitor would not use that ammunition in competition. I know I wouldn't. An excellent example of non linear group dispersion but I would not say it proves All groups fired are non-linear. It only proves there was something wrong with that ammunition. “

LMG< Surely you are not seriously claiming that ammunition that is averaging .5 MOA for 10 shot groups “has something wrong with it” and you wouldn't use it in small bore competition.   Bullets out of a group no further than the bullets in Husker's pictures can't realistically be thought of as “fliers” in the sense that there is probably something wrong with them. This is just what most 10 shot groups look like and should be considered just the natural variation of shots fired unless one knows beforehand, or at the time the trigger is pulled, that something is defective.  

See goodsteel's post #90 and my reply in #91.  We were talking of 5 shot groups but there is nothing magical about ten shot groups that frees them from the same laws of random variation.  These so called fliers also appear in most ten shot groups.  They are usually not as far out or as frequent as in 5-shot groups but they are there.      In my opinion, when we get into talking about core groups and fliers while analyzing results we are often being tempted into trying to make results come out as we hoped they would by disregarding some holes that we don't like.  It is always tempting to do that. That's why we view double blind experiments as the gold standard.     John 

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Larry Gibson posted this 15 January 2016

frnkeore wrote: Linear expansion of the reduced 600 yard, NRA targets.

MR31-100-10 ring . . . . . . . . . 1.75 MR52-200-10 ring . . . . . . . . . 3.79 = 2.166 MR63-300-10 ring . . . . . . . ... 5.85 = 3.343
Frank   Once again your research is lacking in completeness.  Please go back and check the NRA and CMP sites for the description of the reduced targets and why the scoring rings are as they are.  Were you to do so you would find 2 things you missed; first is the score rings themselves are a tudge larger on targets as the range increases.  This is so the scorer can see the spotter and score paddle agree.  Second is if a bullet cuts a score ring it gets the higher score.  The reduced score ring diameter is adjusted for that assuming a .30 caliber bullet hole.  Thus the diameter of the reduced target score rings are is predicated on the actual range to be used at and the use of a .30 caliber bullets.  So if we add .30 caliber to the figures you've posted we find if a .30 caliber bullet just cuts the score ring the actual scoreable moa for each 10 ring is   MR31-100-10 ring . . . . . . . . .2.05  MR52-200-10 ring . . . . . . . . . 4.09 MR63-300-10 ring . . . . . . . ... 6.16   That is as I stated; 2 moa linear scoring.   Now Frank, that is not me whistling Dixie.  That is the rules.   LMG

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Larry Gibson posted this 15 January 2016

John   I have no issue with Lapua what so ever.  Actually I find the test very revealing.  My statement referred to the two groups shown were because of the non linear 100m groups.  It's why I asked Husker if he had any other information on those two groups.  It is those tow I would not use in 50/100 yd/m matches.    Looking at the 15 lots of ammunition tested there are 4 lots I would probably have used in competition as they are indeed moa capable are; (last 4 of the lot #) 2234, 2373, 5143 and 2073.  The average group size for the 15 different lots at 100m is 1.4"  You would lose a lot of points in a match using 22LR in a Match that had an intrinsic accuracy of only 1.4” at 100 yards.  To be competitive the intrinsic accuracy does indeed need to be 1 moa or better as you indicate.  Those are just my observations.   LMG

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Larry Gibson posted this 15 January 2016

John   I spent 4.5 hours at the range today.  Conducted the 7 tests at 300 yards (to be reported later).  I also conducted another 100, 200 and 300 yard test just for you...   Started off with a cold clean bore at 100 yards.  There's 12 shots there.  The 1st fouling shot went high as usual (the target is slightly kitty wampus to the left) and the second fouler is in the group.  I then shot 10 shots for the group.  As we see the group measures right at 1.1".  It is my understanding that sighters are allowed in CBA competitions, right?  If so then is it wrong to use them here in a simple test?   Anyways, here is the 100 yard 10 shot group (actually 11 shots in that group).

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Larry Gibson posted this 15 January 2016

Next was 10 shots at 200 yards, no problem encountered as it's fairly straight forward at 2.2".

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Larry Gibson posted this 15 January 2016

And lastly the 10 shot 300 yard group at 3.35".  Those measurements are taken with that caliper in the photo's which measures to .01” and is plastic and not much more accurate than .01 or so +/-.  Thus we see a 1.1” group at 100 yards, a 2.2” group at 200 yards and 3.35” group at 300 yards....pretty darn close to linear, eh?    All 3 of these 10 shot groups were fired with the same standard load as I posted earlier in this thread with the 20 shot group at 100 yards.  The velocity runs right at 2900 fps with the RPM under the RPM Threshold at 130,500 RPM.  With over 1500 test round through this rifle at velocities from 2300 - 3100+ fps mostly with the 30 XCB bullet I have an idea of what it will do. As I stated in an earlier post shooting groups with linear expansion can be done “on demand".  On another note I found the seven tests at 300 yards with just the weight of the bullet increased .1 gr for each test interesting.  I am correlating the “data” and will post, probably tomorrow.   LMG   LMG

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John Alexander posted this 15 January 2016

LMG wrote: John    Looking at the 15 lots of ammunition tested there are 4 lots I would probably have used in competition as they are indeed moa capable are; (last 4 of the lot #) 2234, 2373, 5143 and 2073.  The average group size for the 15 different lots at 100m is 1.4"  You would lose a lot of points in a match using 22LR in a Match that had an intrinsic accuracy of only 1.4” at 100 yards.  To be competitive the intrinsic accuracy does indeed need to be 1 moa or better as you indicate.  Those are just my observations.   LMG My mistake, I didn't read the table carefully enough.

John

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Larry Gibson posted this 15 January 2016

No sweat John, it happens. Now if Husker has an in to get us some of those 4 lots I mentioned for a reasonable price.......

LMG

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frnkeore posted this 15 January 2016

LMG, "As we see the group measures right at 1.1". It is my understanding that sighters are allowed in CBA competitions, right? If so then is it wrong to use them here in a simple test?"

As usual, you assumptions are not “accurate". If you shoot a fouler on the record target, it will count. In group matches, there is a second target posted for sighter/foulers. On the score target, in the lower left corner, there is a sighter target, clearly marked with a bold print S on both sides of it. You are welcome to shoot all you want in the sighter target but, ALL other shots count.

Frank

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Larry Gibson posted this 15 January 2016

Frank   The topic of this thread is well stated in post #1.

This thread is not about match shooting. This thread is not about intrinsic accuracy, I. E. the smallest group or even shooting for score. This thread is about the point (RPM) where accuracy (whatever that accuracy may be) is lost.  The rifle that I used for the last test has a sporter stock and was not built for match shooting whether for score or for smallest group. This last test was not about the smallest group, it was about demonstrating the linear and non-linear group expansion at longer range concept. That rifle has shot smaller groups at 100 yards BTW. The last test was confirmation (requested by John) of the linear group expansion concept which demonstrated that by controlling the RPM and keeping the RPM under the Threshold very high velocity (2900 fps in this instance) with a naked cast bullet (the 30 XCB while maintaining accuracy (under 2 moa is the expectation but moa accuracy is pretty much the standard with the load used in the 30x60 XCB rifle) that linear group dispersion at longer ranges is easily obtained.  The test results revealed near perfect linear dispersion of the groups occurred from 100 yards to 200 yards and then to 300 yards. 

For several years now I have asked you to conduct a simple test with the '06 having a 10” twist which you profess to have. The test is simple. Simply load a series of incremental loads (1/2 or 1 gr increments)with a fast or medium burning powder (2400 up through 4064 burning rate) with any cast bullet from a velocity of 1400 fps to 2300 fps. Ten shot groups would be nice but you can use 5 shots if you want as the results will be the same. Note the velocity (a chronograph is required as “guestimates” are unreliable) where accuracy begins to deteriorate (that means the groups get larger and larger). Convert that velocity to RPM. After you have completed that simple test then come back here and we can have a positive conversation about the topic.

No one, including me, minds at all if you ask questions. No one minds, including me if you don't believe the RPM Threshold. Everyone is able to make that decision for themselves including me and including you.

Obviously you disagree with the RPM Threshold and that's ok.  The best way to disprove it and to prove I am wrong and my methods is for you to conduct your own test below, through and above the RPM Threshold with what ever rifle you have that is capable.  Simply conduct tests at RPMs from 120,000 to well over 140,000 upwards of 180,000 RPM and prove the RPM Threshold is wrong.  Shouldn't be too hard for an experienced cast bullet shooter like you.

LMG

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frnkeore posted this 15 January 2016

My dear lmg, I wasn't aware that I was under your authority and here to do your bidding. I'm sorry that I stepped outside my bounds :(

But, as always, it's you that that brought this subject to this forum, the title of which is “The RPM Threshold” and is incumbent upon you to prove.

You offer no scientific proof but, ask us to blindly follow you, in your believe that Your threory is real. The thread title isn't even HV cast bullets, again, it's the rpm threshold, everybody else was able to read that.

I've ask you for many years to please do a scientific, blind test, using one rifle and 3 or more idenitical (other that twist) barrels and since we now, can now order people around, I also am saying that it has to be a BLIND test and that you may not do the shooting but, you MAY to the loading of the unmarked, bulk ammo. Oh yea, no sighter shots in the testing results, please :)

I could go on for many more paragraphs but, I'll conclude with this:

Please tell us how these CBA shooters can shoot at 160,000 - 189,000 rpm, with match accuracy and not hunting accuracy as your results have been.

CBA match at Tamaqua, PA

Bottiger, Jerry, Cartidge, 7mm BR - Barrel, Shilen 23” lg, 9 twist - Weight, 12.62 lb - Scope, Weaver 36x

Bullet, NEI 170, Nose .276, Band .285 - Alloy, Lino - Primer, Rem 7 1/2 - Load, Varget 27 gr - Vel, 2000 fps

100 yd, May 2014, ave. of four, five shot groups, 1.395 - June 2014, 100 yd ave. of four, five shot groups 0.774

May, 2014 Charlotte, NC

Galindo, Adolph, Class, UnP - Cartridge 30BR - Barrel, Lilja 22” lg, 8 twist Scope, Leupold 40x - Weight, 22Lb. - Bullet, LBT 180 sp - Alloy, Lino - Nose .304, Base .310 Primer, Fed 205m - Powder Chg, 28.5, Varget - Vel 2100 (189,000 RPM)

Galindo, Adolph UnP 197 8x 100 yd, 193 2x 200 yd, 100/200 Agg 390 10x

Galindo, AdolphUnP 5 shot group, 0.469 100 yd, 200 yd,1.807 100/200 MOA 0.686

Galindo, AdolphUnP 10 shot group, 0.951 100 yd, 3.232 200 yd, 100/200 MOA 1.283

Are these guys, mistaken about what they are shooting or providing untruthful info about their equipment?

Their results where shot at a CBA match and as a CBA member, you may also shoot at a match and have your results recorded. Their groups even had a moving backer for the groups although, I won't insist on that for you.

You see, LMG, that I have a cadre of CBA shooters to do my testing for me. I don't have to fire a shot, nor spend my money on lead, powder and primers to obtain inferiour accuracy.

The rules are simple for this type of presentation, do a scientific, blind test and there will be no doubt. Along with that, you can also bring your equipment to CBA matches and compare it to CBA match results. In that case, other shooters may want to give it a try and further your testing and it's results.

Now my last thought about this is:

You have always called this a “threshold", why is that? A threshold is something that when crossed is different on one side than the other.

Definition: The magnitude or intensity that must be exceeded for a certain reaction, phenomenon, result, or condition to occur or be manifested.

You seem to use it more like a hallway, since it can be “pushed up” (Lengthen) to what ever you want it to be and still not exceeded. My take on it is that if a threshold is crossed, it's different on the other side and you indicate the difference will be less accuracy, not the same and not better as the above info would indicate.

Frank

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HuskerP7M8 posted this 15 January 2016

John Alexander wrote: Husker, This is a check to see if I understand what I think I see in the data you posted.  By being able to measure the same group at both 50 and 100 yards with the Meyton Electronic gadgets, you can see the actual expansion of a single group from 50 to 100 yards.  This eliminates the complication of considering the natural variation of group sizes from one to another when different groups are measured at the two distances. 50 and 100 meters, not yards.  This eliminated the need, and hopeless complication, of needing to consider the concept of the expansion of a “cone of fire” as explained by LMG in post #117. I've only briefly scanned thru some of the discussions in various threads and don't want to risk sticking my foot in my mouth. But, you'll never be able to accurately measure the non-linear dispersion or the other subtleties involved in this phenomenon unless a methodology such as I used is employed. The personal testing and the statistics gathered from match reports here certainly appear to form the basis for a sound hypothesis, but without solid accurate numbers that reduce the statistical uncertainties, I fear you all are severely handicapped in making any type of accurate analysis or forming concrete conclusions.     Have any of you tried shooting through 2 targets simultaneously spaced at 50 yds and 100 yds, or 100 yds and 200 yds? You'll still be at the mercy of shooting in the wind which will skew your results, but you may be able compile superior data. Before Lapua opened their tunnel in Mesa, I tested in my indoor facility by firing through targets located at 25 and 50 yds, but I was always troubled that there may have been some deflection caused by the 1st target affecting shot location on the 2nd target. You wouldn't believe how many BRL (Ballistic Research Lab) reports I read dealing with yaw card deflection equations in order to calculate what my uncertainties were, but I was never comfortable  dealing with a possible source of error I was unable to nail down.    Compounding my problems was the short distance between the targets, but I wasn't willing to accept the greatly increased statistical uncertainties caused by shooter error in an outdoor environment either. Further, your data gives very strong evidence that the expansion of groups is not linear since only one group showed an expansion of being less than proportional to distance (i.e. 1.99.) I rarely, if ever, state “positives” but there's absolutely no doubt in my mind that RF ammo produces non-linear dispersion with increased distance. CF dispersion is linear with distance, but I strongly suspect cast will exhibit the same non-linear dispersion as RF....a “hypothesis".Stated another way for high quality 22rf ammo in a very high quality rifle and under the conditions of the test you report and with a bullet rpm of 47K, group expansion is seldom if ever linear. Because RF is standardized with 16” twist barrels, which in most cases produces Sg factors of approximately 1.5, I've only gathered data for RPM with twists from 16” to 17.5". In other words, RPM's of about 41,000 to 54,000. That means I can't comment on RPM “Thresholds” for cast bullet shooting. I can say that RPM increases dispersion, as well as non-linear dispersion in the range I work with, but that's all. Do I understand what I see? I'd say you understand everything quite well.

“In God we trust; all others must bring data.” “Without data, you're just another person with an opinion.” “If you can't describe what you are doing as a process, you don't know what you're doing.” “It is not enough to do your best, you must know what to do, and then do your best.” W. Edwards Deming (October 14, 1900 - December 20, 1993)

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HuskerP7M8 posted this 15 January 2016

LMG wrote: Husker

Do you know what Lapua's conclusion on the quality of that ammunition was? Not for certain, but Lapua picked the 2954652073 as the best choice for this particular customer. My criteria for making a decision to spend $2,000 to $4,000 for either 1 or 2 cases of ammo is based on the score produced by the 40-shot composite group because it has a higher “Statistical Correlation” to firearm precision than 10-shot group ES's and their averages. If you use group sizes in your testing, you need to use 5 to 7 shots in each group fired to raise that correlation to a level that approaches the more robust/efficient statistics like CEP (Circular Error Probable), EEP (Elliptical Error Probable), RSD (Radial Standard Deviation), etc. What I see in those two targets is a definite 2 - 3 flyers in each group. If we look at the core 100 yard group in each example we see the expansion is linear. Sorry, but there are no fliers or statistical outliers that I can identify in the groups I presented and I fail to see the benefit of looking at the “core” only to form any conclusions when there aren't any shots that fall outside of a 2 Sigma probability ellipse, let alone a 3 Sigma probability ellipse. I think we all should be very wary of describing a shot as a flyer unless we're able to determine where it lies in a normal Gaussian Distribution and/or can calculate the diameter of the probability ellipse it falls outside of. I doubt that Lapua would find that ammunition acceptable for match shooting the 50/100m competitions. Having considerable small bore competition myself ( used an Anschutz Match rifle) experience myself I can say any serious small bore competitor would not use that ammunition in competition. I know I wouldn't. The entire purpose of testing at Eley, Lapua, or RWS is to find a match between barrel and ammo, and it's not to quantify the precision of a firearms system. I usually always exceed the stats from a testing center by a sometimes wide margin when shooting in my tunnel or in competition when the barreled action is installed back into a conventionally bedded stock. With RF it's a misconception to believe rail-guns, and either recoiling or non-recoiling machine rests, produce better results just because they eliminate some of the shooter error. I do employ 2 rail-guns in my tunnel testing but it's very rare for them to match the precision I get with a conventional system. Based on the criteria I described earlier I wouldn't have bought any ammo from the testing session I posted, but I wouldn't necessarily classify it as bad either, if you take into consideration the groups will be in excess of 5% better at yards and an unknown percentage better when the barreled action is back in its stock.   I think I'm getting a little off track with the above, but I'm trying to give some comprehensive answers to your comments and hoping there might be a few of you who find it of interest.   How applicable anything I've said is to cast bullet is debatable, but there are far more similarities between cast and RF than there are differences. Still, I don't want anyone reading what I post to be used as “proof” of anything. Consider it “Food for Thought".  Landy

“In God we trust; all others must bring data.” “Without data, you're just another person with an opinion.” “If you can't describe what you are doing as a process, you don't know what you're doing.” “It is not enough to do your best, you must know what to do, and then do your best.” W. Edwards Deming (October 14, 1900 - December 20, 1993)

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joeb33050 posted this 15 January 2016

HuskerP7M8 wrote: I'd say you understand everything quite well.

Husker; Would you let me have the data for the other ~ 85 groups? Thanks; joe b.

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HuskerP7M8 posted this 15 January 2016

joeb33050 wrote: HuskerP7M8 wrote: I'd say you understand everything quite well.

Husker; Would you let me have the data for the other ~ 85 groups? Thanks; joe b. My apologies Joe, but I'm not quite ready to share all the data yet. Thanks, Landy

“In God we trust; all others must bring data.” “Without data, you're just another person with an opinion.” “If you can't describe what you are doing as a process, you don't know what you're doing.” “It is not enough to do your best, you must know what to do, and then do your best.” W. Edwards Deming (October 14, 1900 - December 20, 1993)

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Larry Gibson posted this 16 January 2016

 

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Larry Gibson posted this 16 January 2016

Time to give this a rest.  Hope I at least answered John's question;  yes John, a lot of actual testing has been done to find where RPM adversely affects accuracy.  The information is there. LMG

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John Alexander posted this 16 January 2016

We are no longer accepting post on this thread. Thanks for your participation. John

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