Flash Hole Diameter’s Effect on Burn Efficiency

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Last Post 01 December 2023

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Wm Cook posted this 25 November 2023

I’ve been working on a project to see the equivalency of SR primed .308 brass to LR primed .308 brass. The initial effort compared LR Lapua with a .079 flash hole to SR Lapua PALMA brass with a .059 flash hole.

Initial results were as you would guess. Faster rifle powder (2400, 4227) shot similar SD/ES while when using medium burn rate powder (RL7, 4895), the SR showed incomplete burn with wide SD/ES. As a side note both the SR & the LR burn rate (SD/ES) deteriorated with slower powder. This was with a .308 Winchester, 205g bullet @ ~1700fps.

Comparing LR/.079 flash hole to SR/.059 flash hole is not comparing apples to apples.

As I’m about ready to embark on incrementally enlarging the flash hole size I thought I would throw out a shout to see if anyone has been down this path before. Thanks, Bill Cook.

A “Measured Response” is as effective as tongue lashing a stuck door.

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rhbrink posted this 25 November 2023

Years ago when I was shooting BPCR the rage was to reduce the primer flash hole and reform the primer pocket to use large pistol primers. I bought a set of dies to do just that and went to work on my 38-55 brass. I will say that you need a very strong press for this along with an anchored bench and strong arms and plenty of fortitude. And it turned out to be an absolute waste of time as near as I could tell. I wasn't much into chronograph work at the time as it's a lot of hit and miss with black powder, too much smoke and stuff flying through the chrony to get a bunch of good readings.

Fast forward to the present time, I decided to get that rifle out of mothballs and shoot it during the Winter months as my favorite breech seating rifle is a pain to work with in the cold. Lube gets cold and stiff along with arthritic fingers, and just too much stuff to fool with to have fun. So, the first box of 38-55 brass that I picked up is the brass that has the reduced primer pockets and flash holes. I have more brass with normal primer flash holes along with large rifle primer pockets. After reading the above statements I will do some load development comparing large flash holes to reduced ones to see if I can detect any difference. Plus, this time around I will be using a scope as compared to the first time I was using iron sights. Eyesight ain't as good as it used to be either.

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Wm Cook posted this 25 November 2023

Thanks Larry. Should have known you've already been there.

Here is a compilation of all the data measured during the test. I’ll be darned if I can see any meaningful difference between the first load with “regular” .061” flash holes and the last test with .140”.

For the LC cases you're using now what size did you drill the flash hole to?
And is it true that the only difference in magnum primers and standard primers is the hardness of the cup?
Did you notice SD/ES deteriorate as the powders got slower?

As always, thanks for sharing your knowledge. You really should write a book. This is as far as I've gotten so far. Bill C.

A “Measured Response” is as effective as tongue lashing a stuck door.

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Larry Gibson posted this 25 November 2023

This may give you a bit of insight. I now use cases with the flash holes drilled out for my 308W cast bullet match loads In LC Match cases, 16.5 gr Alliant 2400, 30 XCB bullets]. The last 10 shot test I chronographed (Oehler M35P gave and ES of 18 fps and an SD of 5 fps.

Drilled Flash Hole High Pressure Test; 308W

In the past I have posted this explanation of why I drill out flash holes for use with low end reduced loads.

“I shoot many thousands of squib loads in various calibers but mostly in .30s. Many of these are rimless cartridges; 30-06, .308, .308 CBC, 7.65, 7.62x39 etc. The squib loads I shoot most often is a Lee 314-90-SWC-TL over 2.7 to 3.2 gr of Bullseye depending on the cartridge. Velocity is around 800 – 875 fps. I found a long time ago the shoulders do in fact get set back with light loads such as those. With many cast loads that use normal weight bullets in the 1600 to 2000 fps range there was little setback. It basically is a matter of the psi the load generates. It takes roughly 7,000 psi (depends on thickness and hardness of the brass along with how much the case needs to reach the chamber walls.

Measurements of shoulder set back or increase are easily taken with a Stoney Point tool. There have been basically the two theories regarding the cause; the firing pin blow theory and the primer theory. I ran the same tests with a fire formed case and inert primers; headspace was not changed. I then used the same fire formed case with live primers. In as little as two firings there was a measurable decrease in headspace. After five live primers the fired primer was noticeably backed out after firing. NOTE: this increase in headspace was with case taking LR primers. I never experience the problem with the .222 Rem or the 5.56 NATO.

Using #d drills I gradually increased the flash hole diameter with a progressively larger drill. Using a different fire formed case with each larger drill and firing 5 primers I then measured the headspace before firing and after. As the size of the flash hole increased the headspace decrease lessoned. With a # 29 drill I no longer got any decrease in headspace. I dedicated five .308 cases and five 30-06 cases that were well fire formed to their respective rifles chambers and drilled the flash holes with the #29 drill. Over the next few days I fired 50 shots with each case. There was an indoor 50” range where I was stationed so it wasn’t all that bad. After the 50 firings there was negligible change in headspace with any of the five cases of each cartridge. The results of my test firmly demonstrated to me that it was the force of the primer explosion that drove the case forward and set back the shoulder. The squib load does not have the pressure to expand the case out to fit the chamber. By drilling out the flash hole the force of the explosion mostly went directly into the case as there is little rim left to contain it. Two other side benefits that were unforeseen; the extreme spread and standard deviations of the velocity readings improved and the case position sensitivity of the small charge was greatly reduced.

As a result of the above tests I dedicated fire formed cases for squib loads for each rifle in rimless cases and drill out the flash holes. I have fired them many, many times now with no further change in headspace. Besides the squib load mentioned I also use 311631 (# may be wrong but it’s the 118 gr GC 32-20 bullet) with Unique in the above cartridges loaded to 1400 fps or so for a little more powerful small game load. The flash hole drilled cases work just fine for those. I now use the flash ole drilled cases for all my rimless cartridges with squib and really light loads.

Further pressure testing in the .308W the last few years indicated that loads with a psi above 12,000 will obdurate sufficiently to prevent the primer from driving the case forward thus setting the shoulder back.”

Since then seems like every time the subject comes up we get admonitions not to do so because it is very “dangerous” should the cases with such drilled out flash holes be used for a “regular” load. Having Previously tested such cases with “regular cast bullets loads creating 28 – 30,000 psi (measured via an Oehler M43 PBL) I have endeavored to ascertain the danger of loading such to the psi of “regular” loads at 55,000 +/- psi.

I had enough cases LC 92 7.62 NATO (308W) cases I was going drill out the flash holes to run a series of 10 tests using five 9 shot tests and five 8 shot tests. I would run a test with the flash holes as they were (.061&rdquo and then increase them in size incrementally to .140”. That is the maximum size to enlarge the flash hole while still retaining enough of a shelf for the primer anvil legs to rest on. I used numbered (#) drills alternately from #44 up through #28 to enlarge the flash holes.

Here we see the cases with the flash holes drilled from “as issued” on the left to #28 drilled on the right;

The cases were FL sized in a RCBS X-die the loaded with pull down M80 bullets (147 gr FMJBT) over 43 gr of IMR 4895 with WLR primers. The loads were tested on 2/25/2019 in my test rifle with a 24” barrel. The Oehler M43 PBL was used to measure velocity, pressure, etc. I could see no difference in the appearance of the primers after firing. Have a look for yourself;

Here is a compilation of all the data measured during the test. I’ll be darned if I can see any meaningful difference between the first load with “regular” .061” flash holes and the last test with .140”.

Throughout the test the sky did not fall, Humpty did not fall off the wall, the chicken made it across the road and no collusion between Trump and the Russians was found………and I’m still alive and the rifle did not blow up……… It appears, based on actual test results, using cases with drilled out flash holes might not be as “dangerous” as some thought………

Completed the 2nd test using 168 MKs over 41.5 gr IMR 4895 yesterday. Shot four 9 shot test groups using the cases with; flash holes as issued, then three other groups with flash holes drilled with #40 drill (.096"), #34 (.111") and #28 (.140"). The results;

With as issued flash holes: 2653 fps SD 16 fps/ES 53 fps; 56,000 psi SD 1,600/ES 4,800; group 1.69"

With #40 drill (.096") drill: 2646 fps SD 9 fps/ES 31 fps; 54,900 psi SD 1,300/ES 4,200; group 1.45"

With #34 drill (.111") drill: 2646 fps SD 19 fps/ES 61 fps; 54,700 psi SD 1,800/ES 6,000; group 1.37"

With #28 drill (.140) drill: 2641 fps SD 12 fps/ES 43 fps; 54,000 psi SD 1,100/ES 3,000; group .945"

The first 2 shots (foulers) were slightly out of the group and gave the 2 highest FPS and psi. That raised the averages above the others slightly. The test rifle normally shoots 10 shots into an average of 1.2 - 1.4".

All the data are once again within the normal test to test variation of the same load. Nothing indicates any "danger" from using cases with drilled flash holes, even with normal high pressure loads with jacketed bullets.

Again, the benefit of using such cases (those with LR primers) is with gallery type loads (cat's sneeze, mouse fart, squib, etc.) that do not generate sufficient psi to obturate the case. Using such cases in push feed actions, especially those with a plunger ejector, w/o drilling the flash holes can lead to shortened case headspace which then leads to failure to fire and/or failure to extract. Drilling the flash holes out alleviates that problem with these type loads.

"I never was concerned about increased pressure of the powder charge from larger flash holes. I do have a mild concern about increased pressure in the primer itself increasing the chance of a blanked or pierced primer."

That is one of the main concerns that is always expressed. If there was greater pressure in the primer with a drilled out flash hole than with a standard flash hole don't you think it would manifest itself in a greater flattening of the primer? Yet we don't see that at all in either test. The flatness of the fired primers regardless of flash hole size is identical. Thus far I have fired 136 cartridges at 56 t0 57,000 psi (measured) w/o a single indication of any greater primer flattening with drilled flash holes vs "standard" flash holes.

Perhaps there actually isn't any greater increase in pressure inside the primer? Or if there is an increase it is not a sufficient increase to pose any problem or danger. There was absolutely no indication there was in increase in pressure inside the primer cups.

A further argument, if not the main argument, against the use of drilled out flash hole cases for gallery loads is that if you inadvertently use them with a standard load it could be dangerous. Thus, if you have a standard load that doesn't pierce or blow the primer and inadvertently use a case with drilled flash holes it appears there really isn't any concern. I am not suggesting whatsoever that full power loads be developed and used with cases having drilled out flash holes……I do not do that. The point of this test was to determine if there is a danger from increased pressure if using a case with a drilled out flash hole.

What I am suggesting is the use of such cases with drilled out flash holes should be used with gallery or other low level cast bullet loads. The purpose of drilling out flash holes for use with gallery or other low level loads is to negate the headspace of the case from shortening with repeated firing from the primer pressure in push feed actions. That is all.

LMG

Concealment is not cover.........

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Larry Gibson posted this 27 November 2023

Wm Cook (Bill)

I've found no indication the size of the flash hole alters the burn rate as such as evidenced by no real change in the psi or time pressure curves. I think what you're really seeking with the reduction of the ES/SDs is an increase in ignition efficiency which the measurement of those should address that. I can also add additional confirmation because when measuring the psi of each shot in a test string the M43 also gives and ES/SD of the measured pressures. Lower and more uniform ES/SDs of the pressure also gives a better measurement of the efficiency of ignition and burning of the powder (not to be confused with "burn rate").

LMG

Concealment is not cover.........

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Wm Cook posted this 28 November 2023

When you get into discussions about weighing/sorting cast bullets and the need to monitor Vel/SD/ES there's going to be knowledgeable people on both sides of the fence in disagreement.

But to me, loading and shooting cast bullets for accuracy is a lot closer to working with a wildcat than it is to jacketed benchrest competition so I approach it that way. It doesn't me right you wrong or visa-versa.

I can only speak from my own experience with accuracy and my innocence in how I approach cast accuracy. Trust me, I have no false allusions that I'll suddenly turn over a rock and find a "the" key to improving cast accuracy. To some of you who have been doing this for decades it must seem like chewing on an old sock when some of these topics comes up.

But for those of us who are new to the concept of cast accuracy we're allowed and I would even say encouraged to question why we're doing what we're doing. To the tenured "been there done that" cast accuracy shooters out there I ask that you jsut be patient with us. I clearly remember a time in the loading room during a competition where an "old hand" was explaining to a new shooter how to find seating depth to the lands. He had a cigarette leaned on his press while he was showing how to look for, measure, shim to get a starting point for olgive to lands. It was like he was explaining to the new guy a quantum theory for evolution. And to the new guy it might have sounded like that Those were the good old days?

Is there a need for fussing over average velocity, extreme spread? It depends. Not if you're competing in IBS or NBRSA competition. No one cared about velocity, ES, SD in 6PPC benchrest competition, in fact I never chronographed a load. We all shot full to full + cases of V133 under a 66 grain custom bullet. The only key variables we could control was how many barrels we could afford and how well we could read the wind.

All jacketed BR shooters used the Culver (Harrell) measure. When I started shooting jacketed BR there weren't any electronic scales in the loading room. They didn't exist. The first palm sized electronic scales arrived in the early 90's as best as I can remember. And they were terrible. Still have a few boxed up somewhere.

I don't have any match reports around from that time period, but shooting in the teens in competition were far and in between. Today's competition will have multiple shooters with agg's in the teens. I don't have the Super Shoot results from this year but in the Stl East West match King and Noel both shot in the .18xx to finish 1st and second in the 100yd light varmint. I'm not crediting better agg's with the advent of the portable electronic powder scales but everyone in jacketed BR has upped their game in the past 20 years. Today's trend is in bullet selection with a lot of shooters making their own ("self").

Then I look at the number of folks that shot sub MOA in this years national and its equally impressive. R Brinkman shot a sub .5" group at 100 yards. In my humble opinion that beats the .18xxx aggs King and Noel shot in the East West jacketed BR match. When conditions are right a jacketed BR shooter will put all 5 shots on record in 10 to 15 seconds. I can't imaging how long it took Richard to breech seat his 5 record rounds. That means that each shot was taken in a different condition. I'm only being partially sarcastically when I say that there are 20 to 1 more variables in cast accuracy than in jacketed.

Most all of us have spent a lot of time with subsonic and wildcats. All my early years was shooting jacketed BR and working with .17, .20 and .22 wildcats (prairie dog shooting). You can't work in that arena without a chronograph. Now think about run of the mill velocities and cast accuracy. Personally I don't see a great difference between a subsonic powder selection/management much different than working with cast velocities in the 1500 - 1700fps range. Whether is wildcats, subsonic or cast there only a limited amount of starting load data to work with. The Lyman load manuals are a positive start for new shooters

I think what you're really seeking with the reduction of the ES/SDs is an increase in ignition efficiency which the measurement of those should address that.

Don't chase the SD god. The SD only tells us what most of the rounds fired will most likely do. The ES, on the other hand test us what all of the rounds have done.

As I started this project I was falling into a pattern of my typical self filling philosophy which at this time was that faster powders (2400, 4227) were going to give better SD/ES than slower powders (RL 7, 4895). On one of my re-checks of a faster powder I shot a five shot string that gave a goofy SD/ES, higher than expected. Looking at the shot to shot variation I found one of the velocities was much lower than the other. I wish I could put my hands on it but can't find the data right now. It made enough of an impact on me that I started to record Vel, SD, ES and each individual shot. At least for the work I'm doing now. That dropped shot wasn't a mistake in loading because I was 10 feet from the bench in an environmentally controlled room.

I'm new so I can be as naive as hell at times. I'm thinking that if I dropped one in a 5 shot string with a powder that I had thought had consistent ignition how many will drop in a 10 shot string or three consecutive 10 shot strings with a powder that gives inconsistent ignition. Will a dropped shot matter at 100, 200 yards. Just depends on how "dropped" the shot was. Or to put it context with what we have been discussing how poor was the ignition efficiency on that particular round or rounds. Not sure about you but I have to click up or down to hold zero if I'm working on load development.

That's what got me looking at case capacity and the ignition efficiency of the powder being used. I'm new enough that I have a hard time accepting fliers. Finding the right powder and improving the ignition efficiency (enlarged flash holes, dacron etc) makes sense to me. We're all different in what we came to believe what is important and what is not important to focus on for accuracy.

The 308 was designed to shoot jacketed bullets in the 2700 - 2800 fps range. Not to shoot cast bullets at 1700fps. That leaves a lot of unused case capacity that has to be managed. So either I have to navigate the ignition efficiency of the powder at 1650 to 1750 in a half filled case or I'll have to head north of 2600 fps and fight the lube / leading ceiling there. I believe that the groups that the 32 Miller's and the 30BR's are shooting might have something to do with ignition efficiency.

And that John A was shooting 5.5g's of Titegroup?

Not looking for a fight here. Everyone has a right to their opinion. And let me go on record and say that I really enjoy Brussels sprouts. Bill C

A “Measured Response” is as effective as tongue lashing a stuck door.

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Pentz posted this 25 November 2023

Conversely John Schauf up in Puyallup has forged the path to smaller flash holes for the 32-20 CPA using Starline brass. He built a swage interior to the case with a exterior anvil to uniform the flash holes to .075/1/16". He's set the 5 shot group record of 0.164 and dominates the matches at Paul Bunyan and Clark Rifles. But I agree with enlarging for the military class and, possibly, others of which I do not use.

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Larry Gibson posted this 28 November 2023

"I may be guilty of a false bias but I think that asking for a consistent, efficient ignition of the powder in a case that is half full of various compositions of medium rate rifle powder is asking a lot"

Bill C

I'm with you in that opinion. By the time we get those medium burning powders up to a psi where they burn efficiently the velocity is most often above where best accuracy will be found in 10" twist 308W barrels. Iin 12 and 13" twist barrels sometimes, depending on bullet mass, we can push up the pressure/velocity a bit and maintain accuracy. Probably not CBA coemption accuracy though.

Best solution I've found, if a medium powder is to be used, is to use a Dacron filler and a heavy for caliber bullet. It's that solution I use when shooting the 7.62x54R cartridge in my Finn M39 in Military Rifle class. I use 4895 under a Dacron filler and a 314299. in the 7.62x54R which is a bit larger than a 308W. Have to say though the ES/SDs still are as good as the match 308W load with 2400 and drilled flash hole cases previously mentioned. My solution was to find a powder that ignited easily and burned consistently. I found that with 2400. It works well when bench shooting as I can control the powder position through my technique of loading the rifle. With field loads (walk about, hunting, etc). where competition level accuracy isn't needed I still favor a medium burning powder, usually 4895, with a Dacron filler. Appears you're leaning toward the faster burning powders for competition use also. Not sure there is a better solution at this time(?).

LMG

Concealment is not cover.........

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Larry Gibson posted this 28 November 2023

I have been chronographing since '74 and pressure/chronograph testing since '07. In that time, I have shot thousands of groups at ranges from 25 and fifty yards [handguns and pistols to 1000+ yards many while chronographing the shots. I have learned several things:

The best consistent accuracy [Note that is consistent time after time, not just one group] will come with low ES/SD data for the specific load. Now, note also I did not say the "lowest" ES/SD. Fact is, as with velocity and pressure measurements there is a variation if the ES/SD as there is a variation of average velocity and pressure. The fact is once you get a CF rifle cartridge load shooting ESs in the 50 fps range or lower, given 10 shot groups. The difference between a 50 fps ES load and 35 fps (example for discussion) will probably not be evident at closer ranges of 300 yards and under. Smaller test/groups of 3 or 5 shots tell little other than what the average velocity oof that load will probably be close to. Even then 3 and 5 shot groups can vary considerably from the true average velocity due to "random selection". BTW, a measured ES/SD of a 10 shot test, or even several tests, of a "load" may not be the true measure of the ES/SD. We know test to test averages vary. Thus, the only way to know the real average velocity with attendant ES/SD would be to test the entire lot of that load. That's not very practical.

The consistent accuracy difference [group size] of a 308W load, cast or jacketed, with an ES of 100 fps as compared to a load having a 50 fps or less ES may not be discernable at 50 or 100 yards but there will be some indications of the difference at 200 yards and for sure at 300 yards given the same components excepting powder and/or powder charge. Those who "work up match loads" at 200 or 300 yards without chronographing weed out the less accurate loads based on groups size. You can bet your bottom dollar, bet the farm or bet your first born had they chronographed those loads they would have found the rejected loads had larger ESs. Those who test only at shorter ranges of 50 or 100 yards can't usually tell any difference although the difference is actually there.

With quality components in an accurate rifle, even at 1000 yards, an ES of 50 - 75 fps (20 shot tests) will shoot excellently in HP competition with a 2 moa 10 ring. However, if shooting in F Class with a 1 moa 10 ring the load used better have an ES of 30 fps +/- if you plan on having equal scores or a tighter group. For best accuracy/precision we want the bullet to exit the barrel at the same barrel vibration "node". The fact is the smaller the ES the closer to same node the bullet will be on muzzle exit. Fact is, of all of the thousands of loads i have tested over the years, the most consistently accurate loads, rifle or handgun with cast or jacketed bullets, have always proven to have the lowest ES/SDs.

Don't chase the SD god. The SD only tells us what most of the rounds fired will most likely do. The ES, on the other hand test us what all of the rounds have done. The SD, in essence is eliminating "flyers". If we consider all the shots will count, we don't want to eliminate any. I've found there should be a correlation between the ES and the SD. The best consistently accurate loads I've tested over the years have had an SD between 20 and 40 % of the ES. Those with smaller SD than 20 - 40 % almost always seemed to produce 1 flyer out of 10 shots. Perhaps, in the group that flyer was all that far "out" but it was still "out".

There seems to be a lower "zone" of ES/SD measurement that if in the load(s) will shoot equally well. This is because there and many other variables that also influence the accuracy/precision of a load. If match shooting or just group shooting at 100 (+) yards the better loads will have ES/SDs down in that lower zone. However, for many other endeavors, we can have loads with pretty large ES/SDs that seemingly perform quite well.

Fact is, the most accurate loads will have low ES/SDs. That is not saying they will have the "lowest". For years we worked up loads measured simply by group size. That's okay as it still works. However, using a chronograph will eliminate some component combinations much more quickly. Chronographing loads, if done correctly, can also provide a lot of useful information. As mentioned previously, my 308W match load has a very low ES/SD. The last chronograph/pressure test of my 7.62x54R Military match load for my SAKO build Finn M39 gave an average velocity of 1836 fps with an ES/SD of 56/18 fps. The psi ran 24,900. The 10 shot test group size was 1.09".

LMG

Concealment is not cover.........

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9.3X62AL posted this 25 November 2023

I haven't done extensive research on this subject matter regarding 'LR vs. SR" and flash hole variance questions. I would need better hardware and a stronger skill set to arrive at any worthwhile conclusions, and others who clearly have what I lack in these regards have already cut this trail. I trust and respect their findings posted above.

I rate myself as a 'Fairly competent' caster and shooter, most of my hobby activities centered on hunting loads and practice ammo for hunting and personal defense. I want as much accuracy as I can get for a reasonable investment in bench time and effort, but everyone's equation varies--depending upon the end goals. Gotta please yourself in this life.

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Wm Cook posted this 26 November 2023

Here's the background data that I pulled out of looking at LR primers vs SR (.059 flash hole primers). This thing started about a month ago when I was getting nervous about ever finding any LR primers. Despite what people have said on the forum, they are still scarce. Local dealers would get a few in but all limited the the quantity to 1000. With the condition of the world today I'm still thinking that we're one unintended international incident away from not seeing any LR primers (bulk, 5000 at a time) for a long spell. Small piston and small rifle came back on the scene, but at a high price. Midway was the first to sell 5000 quantities of LR primers about a few weeks ago and now they are sold out. So thinking that LR primers were an endangered species I wanted to see if sr primers would work for .308 Winchester and 7.62x39.

I'm enamored with Lapua brass since been using it for the past 30 years. When the .308 Palma brass came back in stock I bought a couple hundred and ran the LR vs SR with the .059 flash hole. Just a bit of background here: The Lapua Palma .308 Winchester brass is designed for long range competition with loads such as the Lapua 167g Scenar bullets, 45+g of N150 @ 2800 fps. The small flash hole is intended to shoot the primer charge into the body of a case that is at or near compressed load.

Asking it to improve anything with a case half full or less of faster power was a stretch. Thus I am working toward equalizing the performance of large rifle primers with small rifles. What Larry described was a good moral boost.

With my 308W cast bullet match loads In LC Match cases, 16.5 gr Alliant 2400, 30 XCB bullets]. The last 10 shot test I chronographed (Oehler M35P) gave and ES of 18 fps and an SD of 5 fps.

Attached is the data I pulled together. The first chart was an apology to John who accepted my claim (with just a little skepticism) last October that the powder position was causing my consternation of shooting groups one minute and minutes later shooting patterns. Five would stick and then out of the blue I'd shoot a three and two or a two, two and one!! I blamed it on powder position since I started to using a holding block about the time when things went south. No offense intended for anyone living in the Southern part of the US. But I was wrong. I tested with the powder tilted to the nose, tilted to the base and with the Missouri roll and found virtually no difference in vel or sd.

Pentz comment about John Schauf up in Puyallup was interesting. Previously Bud posted that his cases (32/20?) were about 2/3's filled as I remember and that adds to the conversation of powder position and consistent burn rate with cast bullets. Thanks, Bill.

A “Measured Response” is as effective as tongue lashing a stuck door.

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Wm Cook posted this 27 November 2023

Thanks again Larry.

I have, indeed, used numerous other cartridges of various calibers from using LR primers with the flash holes drilled out. The end result has always been the same; excellent ignition with less powders position "sensitivity"'

This is relevant to what I'm working on and what I asked in the opening post.

I’ve been working on a project to see the equivalency of SR primed .308 brass to LR primed .308 brass. The initial effort compared LR Lapua with a .079 flash hole to SR Lapua PALMA brass with a .059 flash hole. Comparing LR/.079 flash hole to SR/.059 flash hole is not comparing apples to apples. As I’m about ready to embark on incrementally enlarging the flash hole size I thought I would throw out a shout to see if anyone has been down this path before. Thanks, Bill Cook.

This is a good project. First drill out the .059 Lapua Palma brass flash holes to .093 and do a head to head LR & SR to do the SD/ES comparison. Probably using 2400 v 4895. That'll help (at least a little) answer whether SR could replace LR in the .308 case. Then I'll look at the slower burning rifle powders (example Varget, N135) with their LR to LR with their flash holes drilled out (example .111) to see if it effects SD/ES. To date my work with standard Lapua LR brass with .093 flash holes using Varget & N135 didn't look promising. I'm curious to see if I get a better, more consistent burn rate with a larger flash hole.

As a side note. I'm not saying that low SD, minimal ES will = accuracy greater than combinations that may not look as good on paper. At 600 yards it would but not so much at 200yds. But I think its a valid test of the power burn rate. Don't know if this is a controversy in the cast world but I believe that accuracy is based on barrel harmonics.

While my initial focus was on whether the SR primer replace the LR primer in .308 brass the way the thread shaped itself it became a similar question but from a different perspective.

"Can you use the flash hole diameter as a variable to effect powder burn rate +/- to the % of case capacity actually used?"

A .308 case charged with 28 grains of powder fills the cast about 55% for me. 30 BR's in jacketed BR they are running loads with ~35g of 4198 and the 30BR's in Cast BR are using N135 at ~29g. I'm just guessing, because I don't load 30BR, is that the case utilization on the Cast BR side is about 85%??? If I remember right Bud had said his 32-20 case capacity was about 70% and those cartridges shoots some screamers. Bottom line for me is that I don't think a more uniform, more consistent burn rate would ever hurt my accuracy.

MP, sorry but I totally missed the point you were trying to make. Bill C.

A “Measured Response” is as effective as tongue lashing a stuck door.

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MP1886 posted this 28 November 2023

Larry one thing I've done over a lot of decades is study groups that good qualified people have shot their charts show all the nomenclature especilly the ES and SD. More they often, very often, the best accuracy wasn't with the lowest ES and SD's. In experimenting and eventually using slow surplus rifle powders with boosters I believe the efficiency of how well a powder is burning (much like getting the air/fuel ratio precise in internal combustion engines) has more to do with low ES and SD's. In perfecting those slow surplus powders with boosters I can't say my best accuracy came from the lower ED and SD's. I too have done a lot of shooting with the 7.62x54R and much like you with the Lyman 313299, but my choice launhing pad was a Finn 39 made refurbished by SAKO. That rifle shot some might small impressive groups consistently. That was using a boostered surplus powder. I also pressed it to it's limits velocity wise until I got the bullet to keyhole at a very close distance. I still believe it's lack of substantial bearing band length that was the culprit.

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lotech posted this 30 November 2023

John Alexander, there may be a better term than exposed butt, but I don't know what it would be, so let's continue with your descriptor until a more appropriate one surfaces. I've done no formal studies on EB, but I've never found it to be detrimental to good accuracy. I prefer not to use the EB method, however, in working with the very accurate Lyman #314399 design in a .308, I've found EB necessary. I've done extensive load development work with this bullet over a several year period.

I've also done EB work, though considerably less extensive, with other bullet designs (mostly, maybe all .30 cailiber) in other cartridges without adverse affects. Good accuracy has usually been the result. When accuracy wasn't the best, I think I always found an obvious cause that wasn't related to EB.

As for ES and SD numbers, I haven't looked at these in years. I always prefer group size. Perhaps my best consistent groups have low numbers. I don't really know. Many years ago when I did pay attention to these figures, it was diffcult to equate accuracy with low numbers. This was long before these numbers developed a deserved or undeserved fad status. Sometimes accurate loads had low number, sometimes they didn't, sometimes they were in the middle/ inconclusive. As gunwriter Charles Petty mentioned in an article in HANDLOADER some years ago, the numbers are an indication of consistency only, not accuracy. Lots of other factors also affect accuracy.

If all someone wants are low numbers, make up some heavily compressed loads using a slow powder and heavy bullet in a bottleneck case. Numbers will be incredibly low, perhaps the lowest you've ever seen. The load may be accurate or it may not be. No guarantees.

Perhaps I'm far from a perfectionist, but I try hard to enjoy a hobby and shoot the best groups I possibly can without getting eaten up by insignificant factors of questionable usefulness. I'd prefer to channel my efforts toward something that at least appears to be of a worthwhile nature. If your methods work for you, stick with them, but may we all avoid creating dogmatic principles that are not proven.

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Larry Gibson posted this 01 December 2023

Wm Cook

This is what we are try to match up with by developing the lowest ES with appropriately proportioned SD as we can attempting to get the bullets exiting the muzzle at the same point/node. That's the theory anyway..

"this is caused because as the barrel vibrates through its "circular arc" one bullet leaves the muzzle at say 12 o’clock, another at say 4 o’clock and the third at maybe 8 o’clock. The larger the arc of the barrel, the less accurate the rifle will be, and the larger the triangle."

As lotech quotes Charles Petty; "the numbers are an indication of consistency only" which is correct. We are simply trying to obtain the most consistent load (internal ballistics) as we can. Also, as mentioned, accuracy is also dependent on numerous other factors too. Additionally, as i have alluded to, once we get to a certain low ES/SD we find any further lower ES/SDs may not show any improvement in accuracy. So where is that low ES/SD where any lower doesn't matter? Probably hard to put a rule on that one. However, having shot thousands of groups from numerous cartridges in a multitude of rifles while chronographing them since '74 I find once you get a load giving excellent accuracy and having and ES in the range or 30 - 50 fps with and appropriately proportional SD given a 10 shot test string then trying to find any lower ES/SD that gives any better accuracy is often a journey fraught with frustration. Part of the frustration is a different load probably changes the vibrations of the barrel which then probably changes the arc of the muzzle......

LMG

Concealment is not cover.........

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Ken Campbell Iowa posted this 25 November 2023

great stuff guys ... some real shootin goin on here ...

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RicinYakima posted this 25 November 2023

"You gatta please yourself" a great line from Ricky Nelson's Garden Party song.

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Larry Gibson posted this 27 November 2023

MP 1886, you're correct, I have not tested other cartridges as extensively. However, once proven it is no longer "theory" but is fact. I have, indeed, used numerous other cartridges of various calibers from using LR primers with the flash holes drilled out. The end result has always been the same; excellent ignition with less powders position "sensitivity"'. I've never, have had any indication of increased pressure when pressure testing many of those cartridges or just shooting them. Perhaps you have results from such tests you've conducted that demonstrate something otherwise? Or is it just conjecture on your part?

As to shotshells and muzzle loaders; The flash hole in a shotshell is self contained in the primer so there is no flash hole in the shell to drill out. As to muzzle loaders, they don't have cartridge cases let alone primer pockets with flash holes so, again, there's nothing to drill out..........

Here's another test, though not as complete/extensive as the 308W test, I completed about 4 years ago which covers two pistol cartridges. The end results are the same; no increase in pressure with either high pressure or low pressure handgun cartridges.

Drilled Flash Hole Test; 44 Magnum and 45 Colt

Completed the test yesterday 29 April, 2019. Test firearm was a Contender with a 8.4” barrel in 44 Magnum and a 10” barrel in 45 Colt. A 2.5X scope is on the Contender. All measured data except group size (ctc widest shots) was obtained via the Oehler M43 PBL. I had prepared 10 cases, as previously posted, for each test string; 10 with standard flash holes and 10 with the flash holes drilled out with a #28 drill. Winchester WLPs were used in all cases for both cartridges.

Testing was conducted from the bench with a Hoppe’s Pistol Rest with the target at 50 yards.

Temperature was 80 degrees.

Humidity was 30%

Barometric Pressure was 29.63

44 Magnum;

Bullet was a 429360 cast of COWW +2% tin, AC’d and aged 10+ days before sizing .430 and lubed with BAC.

Cases were Remington R-Ps sized and loaded in RCBS dies.

Powder charge; 22 gr of Alliant 2400

OAL; 1.638

With Standard flash holes;

Velocity; 1622 fps (muzzle)

SD/ES; 13/41 fps

Pressure; 35,800 psi(M43)

Pressure SD/ES; 500/1,700 psi

Group; 3.1”

With flash holes drilled;

Velocity; 1599 fps (muzzle)

SD/ES; 17/47 fps

Pressure; 34,500 psi(M43)

Pressure SD/ES; 1,400/3.900 psi

Group; 3.2”

45 Colt:

Bullet was a 452-230-TC cast of COWW +2% tin, AC’d and aged 10+ days before sizing .454 and lubed with BAC.

Cases were CBC 45 Colt sized in RCBS steel FL sizer and loaded in Hornady dies.

Powder charge; 7.3 gr 700X

OAL; 1.598

LMG

Concealment is not cover.........

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Larry Gibson posted this 27 November 2023

"So let me ask you Larry are you talking just using squib loads or are you talking high end high pressur jacketed loads?"

My post addresses the effect of the size of the flash hole in cartridge cases in cat's sneeze/low end pressure loads, "normal" pressure cast bullet loads and high pressure jacketed bullet loads.

The OP, Wm Cook, made it perfectly clear he was discussing the size of flash holes in 308W cases and their effect on efficiency of ignition. You might want to read his first post. Thus, your discussion of shotgun shells and muzzle loaders neither adds information to or proves anything but is simply not relevant to the OPs intended discussion as there is no 308W case used with the powders he mentions in your discussions.

However, if you have meaningful data regarding the OPs actual topic we'd like to see it? Otherwise, along with Wm Cook, I also miss your point.

LMG

Concealment is not cover.........

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Wm Cook posted this 27 November 2023

I think what you're really seeking with the reduction of the ES/SDs is an increase in ignition efficiency which the measurement of those should address that.Lower and more uniform ES/SDs of the pressure also gives a better measurement of the efficiency of ignition and burning of the powder (not to be confused with "burn rate").

That is exactly what I am trying to figure out. I may be guilty of a false bias but I think that asking for a consistent, efficient ignition of the powder in a case that is half full of various compositions of medium rate rifle powder is asking a lot. Again, I greatly appreciate the time you took to point me in the right direction. Bill C.

A “Measured Response” is as effective as tongue lashing a stuck door.

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Larry Gibson posted this 28 November 2023

MP 1886

Not "riled up" at all. You're correct in that your comments had nothing to do with the topic at hand. Have to disagree with the idea "when they design a case, for anything, that they take the flash hole size in mind". Having studied, researched and measured flash holes in many cases over the years I've come to the conclusion "they" just use whatever size of hole their machinery is set up to produce. That machinery probably has a +/- specification to it but that's about all the difference. Probably because "they" long ago that a variation in the size of the flash hole doesn't matter with normal loads for the cartridge.

It is where we use reduced or cat's sneeze loads that the size does matter. That is more than evidenced from Bud Hyett's previous post. Interesting to note on that subject is I've experience hang fires in some cases that were converted to SR Boxer primers from large rifle Berdan primers sch as the 303, the 7.65 and the 7.62x54R. With the powders Bud mentions (RL7, 3031 and 4895) hand fires were encountered with the use of those SR primed cases. The use of a dacron filler, however, negated the problem and ignition is positive and consistent with those powders using reduced cast bullet loads. Ignition is also consistent with very fast burning powders such as Bullseye and Unique w/o a filler.

Actually, I have 4 air rifles already [two 117s, a .20 and a .22] but they are so like last century as they are "springers". That makes them more cheaper than them "one of those new fangled air rifles" cause all I need are the pellets and not tanks, pumps, etc.

LMG

Concealment is not cover.........

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