shape of groups when developing loads

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  • Last Post 18 May 2008
TRKakaCatWhisperer posted this 09 May 2008

I have been puzzling over an observation I make every time I work up a new cast load.

First, the group tends to rise and fall with the load - not too tough to figure - it's a function of recoil and when in the recoil movement the bullet exits the barrel.

Second, the size of the group varies with the charge.  Again not to tough to deal with - just pick the smallest group.

But in the process of watching which groups are large or small and whether they print higher or lower I've noticed three shapes of groups - a scattering, - a horizontal or a vertical shaped grouping.

Observable in 3 or 5 shot groups.

Dr. Mann had some things to say about the resonance of the barrel.

Anyone else observed this?

AND, most important, is there a correlation with size and shape of group?  I.e.: does the smallest group lie between a horzontal group and a vertical group?  Or ...

 

 

 

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runfiverun posted this 09 May 2008

some of your vertical stringing could also be caused by velocity variations

your load is not happy not a bad load just you are not in the pressure zone for thatpowder. with cast in the lower zones some times you need a filler

like dacron it helps hold your powder against the primer also.

you didn't say what cal. your load or bullet, or what your laed mix is.

sometimes you can get variations if you are water quenching by getting a variation in the hardness of your bullet.  this can happen by the temp of your pot fluctuating or by adding lead into the pot that changes the mix.

i try to get a round group then zero in on that one.

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CB posted this 09 May 2008

I find a scattering group to be normal if it shrinks with higher or lower powder charges. During load development, I find each shot should be accounted for especially with a normal scattering. If one shot is in, one shot out, one shot in, one shot out, in other words a center cluster with shots out, there probably is a slight lube problem.

Vertical stringing I've always accounted for a recoil/rest problem.  The only barrel resonance situation I've noticed is a diagonal string usually 7 and 2 o'clock in a right twist barrel. A slight increase in velocity will bring the group in.

The only time I've noticed horizontal grouping is experimenting with cb lubes. Or shooting in a 90 degree cross wind. Of course all load development is shot under ideal conditions, no wind late in the evening or early morning. Every barrel is in different condition along with alloy and today's hi-tech lubes sometime shoot well with just the gap above the gas check lubed....................Dan

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Wally Enga posted this 10 May 2008

Dan,

Good luck in finding those ideal conditions --- I don't think I have been out to the range this year in anything near light wind conditions. :(

 The concept that a strong crosswind component will give you vertical changes is one that some shooters miss and that I have had to re-learn more then a few times myself with lost points.

At 200 Yds, with a 15 mph or so cross wind from the left, I need to come up about 1 ½ mins (3 inches) from my zero wind elevation.  If that cross wind is from the right, I need to come down about the same amount  1 ½ mins (3 inches).

What is really easy to do in a match, is when that with a 15 mph or so left cross wind you are centered on,  then drops off by a lot --- clicking right a few mins will keep you in the 10 ring but if you forget about all that “extra” Up elevation you have in for that strong left cross wind ---- results in a 9 out the top.  Been there, done that. ---- Wally

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RicinYakima posted this 10 May 2008

TRK,

Read with attention to detail the posts of Dan and Wally, as they are right on the money.

I, too, have found the 7 to 2 o'clock spreads as you work around barrel vibrations. This diagonal stringing is a clue that the rifle doesn't like the load. Mann's work is ignored by some folks today, but his principles are valid.

Flat horizontal groups are almost always a mechanical problem or poor trigger control issues. This happened to me once with an '03 that someone had honed through the hardening and a burr was rising causing delayed striker fall.

Wind drift and rise is a factor of sectional density, how long is the bullet for caliber, and velocity loss. Since I have to shoot in the wind almost all the time, I work on loads with the heaviest bullets I can find. This reduces wind drift. The only cravat is that the bullet has to be above the speed of sound by about 50 f/s at the longest range you are going to shoot.

Ric

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TRKakaCatWhisperer posted this 10 May 2008

I've seen this happen in three different calibers (hence 3 different shootin' irons).

This time in a .44Mag Handi rifle with 50/50 WW/lead + a bit o' tin.  This time with a granular filler over the powder, other two times not.  Plain based bullets.

I'll repeat the series soon to see if the group - horizontal string - group - vertical string repeats at the same loadings.  It just caught my attention when I saw 3 or 5 shots side by side or above eachother alternated with larger or smaller groups.  1 grain increments of 4227 14 to 20 grains and 335gr NEI bullet.

Other times included .375 H&H in Ruger #1 and .30-06 in a vintage Springfield '03.

(.375H&H using cast, '03 using jacketed bullets).

 In addition (this was the only time I've seen this) THE first round out of the bbl was high, then low and the next 8 went around in a 1” diamter circle.  I write that off to chance or 'an act of God'.

 

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PETE posted this 11 May 2008

 TRK,

  As far as I'm concerned the first two shots going somewhere else besides the group is fairly normal. Most of my guns will throw the first shot out of a cold clean barrel, and/or a cold fouled barrel, somewhere else. A few guns take two or even three shots to settle down. A very few guns will throw the first shot into the group.

  As has been mentioned here many times.... each gun is a law unto itself. If what you observe happens every time then it's just something you have to take into account when using the gun for target shooting. For hunting you need to know where the first shot out of a cold clean barrel goes.

PETE

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Ed Harris posted this 12 May 2008

Shooting 3 or 5-shot groups isn't enough to tell you if the dispersion is “circular normal” unless you plot x, y coordinates of each shot for a series of groups and calculate the vertical, horizontal and radial variances.

If you don't like crunching numbers just shoot ten-shot groups and look for those with the best central clustering after the bore has become conditioned and has settled down.   There are no “lucky” ten-shot groups.

73 de KE4SKY In Home Mix We Trust From the Home of Ed's Red in "Almost Heaven" West Virginia

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linoww posted this 12 May 2008

If you don't like crunching numbers just shoot ten-shot groups

There are no “lucky” ten-shot groups.

Ditto!

I find multiple 10 shot groups give me more information than a few 5 shot groups.If i get a couple of odd shots within the groups i shoot more 10 shot groups and see if it follows the same pattern.I also find it shows the shape,true center and point of impact changes all at one time ans doesn't “fool you” into measuring a bunch of small 5 shot groups not realizing the subtle POI changes and core group location.

I shot a heavy barrel Savage 99 30-30 in Spokane last month in CBA heavy class.I was having POI/wandering changes and it drove me crazy.I did poorly and shot 181 score and a 1.6"(5 shot groups) average for the 100yd match.I went back looking over all of my nice targets I had shot in practice.I disovered most were 5 shot groups and were slowly progressing to high right each group as the barrel warmed up.The individual groups showed no large vertical tendency though so I got fooled.I hadn't noticed it  before,only the small groups were what i remembered.  

George

"if it was easy we'd let women do it" don't tell my wife I said that!

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CB posted this 12 May 2008

When I develop a load I always shoot 3 fouler/sighters and 10 shots for the group size. Doing it this way I have the most consistant condition that can be duplicated at a match.

Generally, dependant on the wind that given day, I get a somewhat round to oval group. If the wind is a 90 degree cross wind from the right the group moves to the upper right direction due to a condition called “spin drift” when shooting a right hand twist barrel, If it is blowing at 90 degrees from the left, then the group move lower to the left of aim point. The rotation of the bullet causes the bullet to climb and push to the right on a right hand wind and conversely the bullet will be pushed down and left on a left hand wind.  Both caused by the rotational forces of the spin of the bullet.

I read about this in depth once and if I can find the article aI will post it.

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Ken Campbell Iowa posted this 12 May 2008

Jeff Bowles wrote:

The rotation of the bullet causes the bullet to climb and push to the right on a right hand wind and conversely the bullet will be pushed down and left on a left hand wind.  Both caused by the rotational forces of the spin of the bullet.

I find that a true  wind from the right ( every flag on the range shows a from-the-right wind ) will usually blow a bullet to the leftish ... somewhat, and usually ... (g) ... unless of course there is a tree, gulley, or berm within a hundred yards of the bullet path .. (g) ... aint this wind surfing fun ? ken campbell, ia

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TRKakaCatWhisperer posted this 13 May 2008

I am lucky to be able to shoot at a National Forrest range tucked in against the leeward side of a small mountain.  Wind is a rarity.  However at Quanitco I've seen wind flags blowing in every direction, sometimes towards eachother!

Too much rain, haven't gotten out this last weekend.  Prepared much more brass.

 

 

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CB posted this 13 May 2008

Oh yeah wind surfing is a blast! Of course that is the challenge of the game! Although there are time I wish that aspect of the game would fade away... I have a feeling this will be a windy year and little bitty groups will be rare to non-exisitant.

Ken you are correct with what you say about the bullet getting pushed left, unless you are shooting a Washtenaw... We have the weirdest wind effects I have ever seen. That is why I enjoy going to other ranges that have less geographic effects than my range.

If you can shoot good at my range, you will shoot good anywhere!

Mirror, mirror on the wall, who has the worst range of them all??

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sundog posted this 13 May 2008

I think Ed is correct about number of shots.  Five is not enough.  Five can be enough to tell if you are on track, but to really see what's happening, the number should be ten of more.  Our milbolt matches here in Oklahoma include two 10-round group targets.  Ten rounds can sure separate the technical shooters from the casual shooters -- in a hurry.

Y'all already hashed around about the wind.  So much for horizontal dispersion.

But, depending on your sights (and your eyes) you will get other types of dispersion, such as vertical stringing typical with milsurps with a front post.  In other words, it's all relative.

I have a couple more thoughts.  Sometimes the best you're gonna get is X moa.  It might be all the gun is capable of.  The other thing is that when you find accuracy, it needs to be consistent over a range of conditions, and repeatable day in and day out.  On demand.  Otherwise it is not accurate.  Just thinkin' out load...

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codarnall posted this 13 May 2008

Just got my CBA CAST BULLETS by Brennan,Jr.   well worth joining CBA for it.  Therein is the  only other time I've read that 10 shot groups are not significantly more telling than 5 shot groups.  The other place was Rifile Accuracy Facts by Harold Vaughn,  a scientist at Sandia National Labs. in Albuquerque.  How the powder lay in the case in large capacity rounds is probably the largest factor in vertical  or any dispersion in general.  I have found barrel whip is far less troubling in light loads than FMJ's and their 40K+ pressures.

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TRKakaCatWhisperer posted this 14 May 2008

Still raining here.

It's been a good time to process empty brass.

Good collection of principles here.

 

I generally run 3-5 shots on my FIRST cut through the loading range.  Patterns generally run in cycles from large to small to large to small.

THEN when a narrower range of loads shows promise work up to 5-10 shots at smaller  differences in loading and then to verify - find a load that will do at least 3 to 5 five shot groups in a row.

Of note here is the relationship of the magnatude of variation due to each source of variation.

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Ken Campbell Iowa posted this 14 May 2008

Hi Er'One....   In bringing up the following thoughts ... I feel like the guy who steps in your pie at a picnic ....  but ::

When talking about group sizes and shapes, keep in mind the effects of the tuner device that maybe you should be using before passing judgements on ” bad loads” or ” good loads” ....

Every year or two I note that some energetic soul tests every brand of .22 rimfire available and writes the report up in Precision Shooting ... but neglects to use a tuner, as admittedly that further adds complication that gives Migraines ....  IMNSHO (g) the test is only partially valid ......   there is a huge chance that ammo ( loads ) that could be very very good ( best of the bunch ) but don

I realize that much of our cast bullet shooting pleasure is based on nostalgia, and most of are NO WAY going to stick something that tends to look like part of a dog's anatomy ... on the end of a perfectly good Ruger 1 or ( yuk ) a Winchester 94  ..... but still, when talking in theoreticals, such as this thread, we should keep in mind that we are talking about our wonderful family but neglecting the ugly brother that the folks keep locked in the basement. 

Sorry to bring this up, but keep  in mind next time your are “working up a load” that there is something missing if you are not using a tuner.

regards, ken campbell, tuning up in Iowa

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TRKakaCatWhisperer posted this 14 May 2008

Thanks, Ken, for bringing this back to the original question.

I have not experimented at all with tuners, although I firmly believe in their efficacy.

Well worth much pondering and planning of the parameters of the next experiment.

 

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RicinYakima posted this 15 May 2008

Tricks of the trade for those that believe in five shot groups.

Hang your first target and shoot your five shot group. Then, matching corners, place your next target over the first one. Continue for at least 5 five shot groups. Or hang #2, shoot, and remove and hang #3 over #1.

Now spread all the targets out, and measure and analysis. There is a lot of luck in shooting a small five shot group. That is the reason bench-rest matches place so much emphasis on aggregates for determining who shot best on match day.

Ric

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TRKakaCatWhisperer posted this 15 May 2008

Sometimes the SIMPLE things are the most valuable.  THANKS for the tip!

That also has application in load development.

 

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linoww posted this 15 May 2008

Hang your first target and shoot your five shot group. Then, matching corners, place your next target over the first one. Continue for at least 5 five shot groups. Or hang #2, shoot, and remove and hang #3 over #1.

 

You can do the same thing by shooting at gridded paper and doing an overlay on a blank target (with dots for each bullet hole) on a “master” target.The grids help you square up and center of your aiming point better.If you use different colored pens to plot holes you can watch the groups movement(or not) during the shooting cycle.Boring but useful.

Rics method is simpler and works well,but I can do this “plot" system when i get home.It also allows you to see individual holes rather than one torn center on a backer target.I can also stay at the bench rather than walking down and hanging targets over the other for each group.But that sometimes is a downfall as I tend to shoot too rapidly with multiple aiming points waiting to be shot at.

 

George

 

"if it was easy we'd let women do it" don't tell my wife I said that!

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RicinYakima posted this 15 May 2008

George, “one torn out center"? Gee, I never shot that small of groups in my life!;)

Ric

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TRKakaCatWhisperer posted this 16 May 2008

RicinYakima wrote: George, “one torn out center"? Gee, I never shot that small of groups in my life!;)

Ric Two ways it could be done :) : small groups OR LOTS of bullets. 

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linoww posted this 16 May 2008

George, “one torn out center"?

Let me lie a bit<G>

 Gee, I never shot that small of groups in my life! Ric

I know Joe keeps me updated<G>Although I hear your .32 Bunny Gun is starting to shoot well.

Two ways it could be done  : small groups OR LOTS of bullets

Lots of bullets.

 

George

 

"if it was easy we'd let women do it" don't tell my wife I said that!

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CB posted this 18 May 2008

It seems to me that there is no right number of shots for a group. Any number per group will give you information if you analyze the results correctly and are honest with yourself. Some like five shots. Some like ten shots. Some like Fords. Some like Chevys.

There IS, of course, such a thing as a lucky ten shot group you just have to shoot more groups to find one. Same with twenty shot groups or ---.

Whether shots per group make a difference depends on what you are trying to find.

If you are trying to determine what we usually call accuracy of the rifle/load, then:

If you shoot ENOUGH five shot groups and they average 1.0 MOA -AND the point of impact isn't shifting, you can predict that an average of enough ten shot groups will be about 1.24 MOA and an average of enough three shot groups will be about 0.81 MOA. That's just statistics.

The trick is shooting ENOUGH which we often don't have the patience to do. “Enough” is about the same number of total shots no matter how many shots are in the individual groups.

One problem with shooting three ten shot groups instead of six five shot groups is that a flier or two caused not by the rifle or load but by bad hold, wind, tired eyes etc. has a disproportionate effect on the average, and makes the rifle/load look worse than it really is.

If you are checking for round groups or what Joe Brennan calls “in control", then ten shots are better than five shots and twenty are better than ten.

I like Rick's method of shooting the first five shot group again while shooting the second one. I have also used the plotting method to see what the composite group looked like.

Of course if you are a gun writer testing and writing about a new rifle for one of the popular gun mags, then three shot groups are clearly best (two would be better yet).

Then you can show a picture of the best group found and use phrases like, “when I did my part” or “the rifle wanted to shoot” and other such horse hocky and the gun manufacturer will be happy and continue to advertise in you publication making your boss happy, thus three shots are best.

John

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CB posted this 18 May 2008

Ric

Sorry about mistyping your name.

John

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hunterspistol posted this 18 May 2008

  I'm by no means the official version, no authority on the subject at all. I just spent another six months doing load development for a 32-20 TC with a 10” barrel, along with a 7mmTCU that I'm not finished with.  The 7mm is a 10” barrel also, that means that every slight change makes a Drastic difference!

Most of my horizontal spreads seem to be rather circular caused by inaccuracy of the powder load, or mostly my fault-trigger pull!  The vertical has presented itself in full glory on the 7TCU.  When the powder gets hot enough to reach farther, the bullet climbs about 6-8 inches-grouping in the center of a white spot.

My load development for these short barrels goes from one tenth grain measurement to the other.  In other words, for a five shot group with one-half grain difference, I've shot 25 rounds. So, the entire load-finding process may take up 200 rounds or more. I'm glad the range is near my home-I've never lost sight of how lucky I am.

Here's the photo of what I've come up with since last year-scale size? These groups are somewhere in 1&1/2” range, the cards are 5X8” so, I'm getting down to real groups.  The black spots are the size of a quarter(that's the pattern for the target).

By the way, these are from 100 meters, 109 yards on a silhouette range.

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