Is drilling out flash holes dangerous?

[Larry Gibson]

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”) 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;

237040

The cases were FL sized in a RCBS X-die the loaded with pull down M80 bullets (147 gr FMJBT) ove 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;

237041

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”.

237042

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………

[LazyTCross]

Well conducted and interesting test results. I enjoyed the read.


Sent from my iPhone using Tapatalk

[DougGuy]

I would think the only real difference could be in how far the brisance of the primer could reach into the powder. It would seem that with the factory primer hole the pressure built up in the primer would push it farther into the powder than it would if the primer hole was large.

[Larry Gibson]

We might think that Doug but there is no measurable indication of that. Should that occur and there be some change it would show up in the "Rise" measurement. Note there is no consistent change + or - as the diameter of the flash hole increases. Also there is only a 15 micro-second difference between the high (test 5) and the low (test 8). That is only 15 millionths of a second. Note also the largest diameter flash hole is only 4 micro-seconds slower. BTW; "rise" is the a measurement of the efficiency of the powder burn. It measures from 25% up to 75% of the rise in pressure.

[Conditor22]

LG, I really enjoy your posts and tests. I always learn so much from you and OP75.

Thank You

[rsrocket1]

Excellent test and data. I'm surprised at the high ES and SD peak pressures on the 0.140" flash hole test. I wonder if the huge swings are due to the size of the flash hole or if it made it more sensitive to powder position (averaging out to a reasonable number). Were your measured peaks from 52-60 kpsi?

[brass410]

Thanks Mr G as always well documented I have been wondering about what would happen if by chance I got some of my brass mixed erroneously and had drilled them now I know . I've just learned something new today!!!

[dverna]

The largest flash hole results show a high ES and SD in psi. Was there one "outlier" that caused that or were the readings erratic?

[kungfustyle]

As always, Great stuff. I noticed that the groups were in the 2 to 3" range, is that standard for the rifle or does it shoot better with the as issued primers holes? I wonder if a slower/faster powder would change the group size?

[Larry Gibson]

Excellent test and data. I'm surprised at the high ES and SD peak pressures on the 0.140" flash hole test. I wonder if the huge swings are due to the size of the flash hole or if it made it more sensitive to powder position (averaging out to a reasonable number). Were your measured peaks from 52-60 kpsi?

Actually there was one that gave the highest psi and velocity. Had not the other 7 shots been within the normal range for this load I would have suspected something. The same thing occurred with load #5 with it's 37 fps SD and 90 fps ES. That load also had one high psi and velocity. I suspect I may not have gotten all the steel jacketed M80 bullets out. Don't know though. The peak psi for #10 was 61,400 and the low was 53,000 psi.

[Larry Gibson]

The largest flash hole results show a high ES and SD in psi. Was there one "outlier" that caused that or were the readings erratic?

Yes, there was also one very close to the same in test #5 as explained above.

[Larry Gibson]

As always, Great stuff. I noticed that the groups were in the 2 to 3" range, is that standard for the rifle or does it shoot better with the as issued primers holes? I wonder if a slower/faster powder would change the group size?

The test groups were with pull down M80 bullets. I tried to remove all the steel jacketed ones but may have missed a couple. The brass jacketed ones are all from different lots and different bullet making machines. They shoot consistently into 2 1/2 to 3" groups with an occasional flyer out of that, as seen in test #6, with 10 shot groups. The average group size of 2.79 is well within the norm for those bullets.

I did shoot a validation 10 shot test string just prior to this test to validate the rifle/Oehler were working within normal limits. I used a match load of the Sierra 168 MK over 41.5 gr H4895 with WLR primers in LC Match 72 cases. The 10 shots went into .91" which is about right for that barrel. The velocity was 2699 fps with an SD of 9 fps and an ES of 25 fps. The average PSI was 58,800 with an SD of 700 psi and an ES of 2,100 psi. That was almost exactly as it should be. All was well with the system.

When I was loading for the test I was thinking of just internal ballistics but now, on second thought, I wish I would have used a better quality bullet.......:-?

[edp2k]

Any evidence of the primer backing out more with the larger flash holes?

[slim1836]

Larry, I could only wish I knew what you've forgotten, providing you actually forget. Thanks for making my brain think, always enjoy your posts.

Slim

[M-Tecs]

Any evidence of the primer backing out more with the larger flash holes?

It would be less. Primers backing out is only a issue with low pressure loads. The solution is larger flash holes. On normal loads the primer gets reseated.

[RedlegEd]

Larry,
Great write up. I was really interested in the #41 drill bit since that's the size Spence Wolf recommends drilling out .45-70 primer holes for Trapdoor loads. It seems the data for that size hole (0.096") falls right about in the middle of your data and might be a general all around good choice for enlarging primer holes for a variety of loads.
Ed

[smoked turkey]

Thank you Larry for the very informative posts (as always). I have read the various arguments/theories on larger primer pocket flash channels and it is good to see something concrete about it. I also learned something new today right here!. Thanks.

[dverna]

Agree...good post!!

It makes me wonder how the standard size flash hole was originally determined.

[243winxb]

https://apps.dtic.mil/docs/citations/ADA606635

Influence of Berdan and Boxer Primer Spit-Hole Diameter on 7.62-mm Cartridge Performance.

The U.S. Army Research Laboratory (ARL) conducted a study to examine the effects of varying a small caliber (7.62 mm) cartridge s spit-hole on the interior and exterior ballistic performance of the cartridge. Along with standard Boxer primers, a Berdan style primer configuration is evaluated. Performance metrics evaluated were cartridge pressure, primer pocket pressure, and muzzle velocity

EDIT-
The pressure in the primer
pocket is calculated to be approximately 23,890 psi

My Savage Axis will set the 223 shoulder back .006" from 1 pin strike. More with the 2nd hit. Using a dead primer. The extractor type allows the forward movement.


Search at https://discover.dtic.mil

[243winxb]

https://apps.dtic.mil/docs/citations/ADA622138

Primer Output and Initial Projectile Motion for 5.56- and 7.62-mm Ammunition

I had primers fire and the bullets didnt move at all.

1. No powder in a 30-06.

2. H450 powder started burning and stopped in a 22-250 using a cci mag primer.

[SvenLindquist]

So if low pressure causes shoulder setback what about these 2 ideas:
1. use magnum primers ?
2. seat the boolit out enough to engage the rifling ?

[Larry Gibson]

It's not the low pressure that causes the shoulder set back. It is not enough pressure to expand the case (it takes upwards of 7,000 psi +/- to expand a case to seal against the chamber walls) and thus it is the force of the primers psi inside the primer pocket driving the case forward setting the shoulder back a bit with each firing. Magnum primers will only exacerbate the problem. Seating the bullet out (if you are using a long enough bullet) to engage the rifling can help a bit but shoulder set back will still happen after several firings.

Keep in mind this cartridge case headspace set back occurs most often with "cat's sneeze" or "gallery" loads with light for caliber bullets and very small charges of powder. Similar to or the same as using 3.2 gr of Bullseye in an '06 case with a 90 - 100 gr cast bullet. The problem is usually results in misfires or failure to extract in push feed actions. CRF actions allow only as much case headspace setback as the extractor, which holds the case back, allows.

[Bloodman14]

Mr. Gibson, I had indeed asked this question concerning shoulder set-back in the Case forming section; some answers made sense, some didn't. Thank you for putting in the time and effort to answer this question in a definitive and cohesive manner!:awesome:

[SvenLindquist]

If you load boolits to engage the rifling, they will always work, regardless of the case shoulder position.

[Larry Gibson]

If you load boolits to engage the rifling, they will always work, regardless of the case shoulder position.

Not necessarily so. In a push feed with a stiff ejector spring the ejector pushing the case forward and the tension of the edge of the extractor pushing the case forward forward can seat the bullet deeper pushing the case (with short headspace) farther into the chamber without the extractor snapping over the rim. It may fire or it may not but if the extractor is not over the rim it will not extract. Been there, done that......

Also with the short pistol length/weight bullets most often used in these type loads seating the bullet to engage the rifling is not practical. And even if doing so the bullet does engage the leade the headspace of the case will still shorten after several firings.

[243winxb]

Post #40 http://forum.accurateshooter.com/threads/primer-output-pushes-bullets-into-rifling.3966017/
237074

#41 primer.- The pressure in the primer
pocket is calculated to be approximately 23,890 psi

A primer may have to much output, moving the bullet too soon. This may cause a secondary pressure spike. Some combinations of components may be dangerous, depending on the nitro content in the powder. The reaction is similar to a plugged bore. IMO.

[Dale53]

Larry;
Thank you again for the fine report!

Dale53

[243winxb]

Mr Gibson, love your testing. Always great info.

Question- Will a primer alone, no powder, push the Lee 314-90-SWC-TL out the end of the barrel?

[Mr Peabody]

Thank You for the time and effort to do this!

[swheeler]

Larry good test, I often wondered about the warnings posted of accidentally loading a full pressure load in drilled brass being dangerous. I do find the pressure and velocity of 43 gr IMR 4350 with a 150 gr bullet in the 308 to be higher than I would have expected.

[bedbugbilly]

A very interesting read - thank you for sharing! Am copying it off to put in my shooting notebook. Well done!

[Windwalker 45acp]

tagged for more-in-depth reading later.

Thanks Mr. Gibson for researching this. I've done this in the past only on 45acp and the reason being was to match Federals largish flash holes by enlarging winchesters relatively smaller holes(range pick up).

[Larry Gibson]

Mr Gibson, love your testing. Always great info.

Question- Will a primer alone, no powder, push the Lee 314-90-SWC-TL out the end of the barrel?

No........well maybe if loaded in a .308W and shot in a .358W.........[smilie=l:

I've found the best load when using Bullseye with that bullet is 2.7 gr in cartridges with case capacity up to the 300 Savage and 3.2 gr in cases from the 300 Savage up through the 30-06. Velocity will run 800 - 900 +/- depending on barrel length and case capacity.

[pjames32]

Good information Larry. Thanks for your testing and your explanation. I appreciate your sharing your knowledge.

[DDriller]

Thank you for the write up Larry. Kinda makes you re-think uniforming flash holes for accuracy.

[woodbutcher]

:D Hi Mr.Gibson.Thanks for another interesting and informative write up.Thank you.
Good luck.Have fun.Be safe.
Leo

[eric123]

Thank you for your work on this....

[Rattlesnake Charlie]

Thanks Larry for empirical evidence on this subject.

I've often thought that the diameter of the flash hole made little difference in pressure that the primer cup experienced. The affect on the powder charge, that is another matter, especially when considering black powder. More to come on this splinter. Now, to work on my .45-70 black power and duplex smokeless loads....

[T_McD]

Couple of questions for you and forgive my ignorance as I am not 100% sure I understand the problem you’re solving.

1) this problem is negated by the firing of standard loads every once in a while, correct?

2) do you, or anyone else know why flas holes are the size they are. Is it by design, or just a manufacturing process

[243winxb]

https://scholarsmine.mst.edu/cgi/viewcontent.cgi?article=8415&context=masters_theses

Ammunition manufacturer Fiocchi of America solicited this research in order to
potentially improve their manufacturing process as well as their product. By seeing the
effects of flash hole variations on the end use of the cartridge, Fiocchi would be able to
see if changes are needed.

Long- Looks like an all day read.
Its a long read. Conclusion is on page 115. Powder used for both 223/308 was WC 749.

https://scholarsmine.mst.edu/cgi/viewcontent.cgi?article=8415&context=masters_theses

Quotes - Pressure seems to climb to a peak and then fall as flash hole diameter increases in each caliber. This peak occurs at the 2.4mm flash hole on the .223 Remington plot and at the 2.8mm flash hole on the .308 Winchester plot.

It is shown that as flash hole diameter increases above 2.0mm, there is a decrease in group size (i.e. an improvement in precision). Both calibers have the 3.0mm flash hole having the best precision amongst the 4 other flash hole diameters tested. The 3.0mm flash hole values for each caliber also have relatively small standard deviations compared to the other diameters.

The 2.4mm and 2.8mm diameter peaks seen in the .223 and .308 calibers, respectively, could be the ideal flash hole diameters for each caliber.

For both .223 and .308 calibers, the 3mm flash hole diameter group size decreased by 20% when compared to the 2mm flash hole diameter control. This decrease was the greatest of all the other diameters and was accompanied with small standard deviations for the 3mm flash hole diameter values. Although there was a decrease in group size for flash hole diameters greater than 2mm, all but the 3mm diameter had large standard deviations. Further testing on the 3mm flash hole diameter would be required to confirm these findings.

237159

Change powder and/or primer and my guess is, result may be different?

[Finn45Colt]

Mr Gibson, love your testing. Always great info.

Question- Will a primer alone, no powder, push the Lee 314-90-SWC-TL out the end of the barrel?

I just had to test it now for the sake of sciense: 7,62x39 S&B brass, CCI LR primer did push Lee 90gr SWC out from brass 3/8" to the barrel.. Added 0.6gr VV N310(=Reddot) and boolit came out complety. Shot it to pillow and only rifling marks. Rifle was single shot Baikal with 16" inside chromed barrel from lightmachinegun.

[243winxb]

I just had to test it now for the sake of sciense: 7,62x39 S&B brass, CCI LR primer did push Lee 90gr SWC out from brass 3/8" to the barrel.. Added 0.6gr VV N310(=Reddot) and boolit came out complety. Shot it to pillow and only rifling marks. Rifle was single shot Baikal with 16" inside chromed barrel from lightmachinegun.

Good to know, Ty.

[Larry Gibson]

Definitely an interesting read, yes I read it all.

I found it to be a well thought out, well conducted and well documented test. That was as it should have been for a master degree thesis. What I disagreed with was the exclusion of the "outliers" (the shot data that lies outside the norm determined by the Interquartile Range (IQR) method). I disagree with doing that because we, as shooters, never know which round may or may not be an "outlier". If we shoot an outlier without the use of the chronograph and/or pressure measurement how do we know it was an "outlier"? We don't and we must accept the result [score, miss, wounded animal or even worse] of every round fired, factory or reload, whether "normal" or an "outlier". IMHO if we are to strive for the most uniform consistency in our reloads we include every shot.

I was also disappointed [given the .308W rebarreled M788, the semi machine rest and the quality bullets used] of the poor accuracy obtained regardless of flash hole size or location. Based on the moa size and the targets it was obvious the accuracy was worse than I obtained using pull down M80 bullets and shooting from a standard bench position w/o aid of the semi machine rest. The accuracy should have been much better, given the equipment used, and I would not have made the same conclusions or any conclusions at all regarding accuracy potential of flash hole size or location based on his resulting accuracy with the 308W M788 rifle. Something was amiss with the set up and execution of the accuracy testing.

I made no conclusion regarding accuracy in my test even though I included the group size simply because of the quality of bullets and the expected group size variation based simply on that lower quality. I may run an accuracy test with the .061, the .108 and the .140" size flash holes using the 168 Sierra MK over 41.5 gr H4895 in the same rifle.

[Hossfly]

So the answer to this question of, is drilling out flash holes dangerous, is (no), as long as you use common sense. Don’t go too big, leave enough I’d wall to hold primer securily, and keep as centered as possible. If you mark the Case’s and use only for squib or cat sneeze loads, if you mix up with other cases and load to full power, your not going to blow up your rifle. Great job LG, for your testing and showing the results. 243winxb thanks for that link very long and a lot of data to consume, filed it in Adobe for reference later.

[243winxb]

My link info would have been better if a benchrest type rail gun was used for accuracy. And as said, better components. Who has that powder? Not i.

I agree with Larry's post.

[Hossfly]

From looking at the targets on the .223 they do good as long as they are centered. Haven’t looked close at the .308 yet. When their drilled off center then they spread out.

[Hossfly]

Looking at the .308 targets, they don’t seem to be affected as much by off center flash hole as the .223. Maybe because of case capacity? Or moving into fall with temps. Changing I don’t know.

[oldblinddog]

I may run an accuracy test with the .061, the .108 and the .140" size flash holes using the 168 Sierra MK over 41.5 gr H4895 in the same rifle.

I suggest, if you have the time and inclination, that you also test 41.5 gr AR-COMP as well.

[T_McD]

1) this problem is negated by the firing of standard loads every once in a while, correct?



Is this accurate??

[Larry Gibson]

1) this problem is negated by the firing of standard loads every once in a while, correct?

It can be.

Whether or not will depend on what "every once in a while" means to you. If there is little case headspace shortness then they will probably fire form back to full case headspace fit to the chamber.

However, if the low end loads have created enough of a case headspace shortness then firing them with a "standard load", especially a jacketed bullet standard load, can cause incipient case head separation. While not especially dangerous per se incipient case head separation can result in the front part of the case stuck in the chamber and, possibly, some gas cutting of the chamber.

[T_McD]

Thanks

[243winxb]

Larry, do cast rifle bullet loads benefit from a crimp ? Crimp is the first thing the military tested with this 7.62 ammo. https://apps.dtic.mil/docs/citations/ADA341390

An engineering study was conducted on the 7.62 mm ball cartridge, M80, to determine the cause of a recurring delayed propellant ignition and to identify possible causes of action to correct the problem

[Larry Gibson]

From one graph taken out of context with the whole study really tells me nothing because it's hard to understand what it's supposed to represent or show. That's especially the case when the "reference" ammunition used has a 379 fps SD at ambient temperature and then the rest of the test (whatever it's objective was) is done at -65 and + 125 degrees with no observable correlation of the results.

But to answer the question; "do cast rifle bullet loads benefit [I'm assuming by "benefit" you mean better ignition] from a crimp?" ........ in rare circumstance, yes........ most often no. In reference to part of this threads topic (cartridge headspace with cat's sneeze/gallery loads) crimping the case mouth into the bullet will have no effect or "benefit" in reducing the shoulder setback from the primer firing.

[P Flados]

This test was a great demonstration of "myth busting".

However, I am not sure it is applicable to all combinations of gun and load.

When messing around with primers, most of my loads seem pretty insensitive to a primer changes.

However, there are examples where loads are much more primer sensitive.

The most common would probably be magnum pistol loads with hard to ignite ball powder and light bullets. It is my understanding that these need a "hot" primer.

Very small capacity rifle cases (22 hornet) are a second interesting group. Some folks find that they have to use small pistol primers to get best results.

[dale2242]

Good job Larry.
What a great read.
Have ever thought about joining 'Myth Busters"?

[Larry Gibson]

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.

[Hossfly]

Larry it looks like the drilled flash holes will be fine Even if you get them mixed in with issued ones by mistake. Looks like it even will reduce SD with pressure dropping some see no danger making these mouse loads at all, and may even improvement over issue. Thanks for doing these test very helpful.


Sent from my iPhone using Tapatalk

[Jniedbalski]

Iam glad you did this test. I always have read that if you used enlarged flash holes it would creat dangerous pressure with a regular loads. Glad you found out differnt

[Elkins45]

Excellent info. Thank you for taking the time to do the research and to post it.

[M-Tecs]

http://bulletin.accurateshooter.com/2013/05/large-vs-small-flash-holes-in-308-win-brass/

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. I have no idea if there is a difference between a .059" a .080" or larger. I do know on smokeless muzzleloaders that use .032" vent liners if you let the vent erode too much you start over pressuring the 209 primer.

[Bloodman14]

Just thinking mechanically, M-Tecs, I would think that with a drilled-out flash hole, the pressure on the primer would be less. Can't address the smokeless/209 issue.

[M-Tecs]

Just thinking mechanically, M-Tecs, I would think that with a drilled-out flash hole, the pressure on the primer would be less. Can't address the smokeless/209 issue.

Same cartridges are 65,000 PSI SAAMI. Priming compound will not produce 65K. With the smokeless muzzloaders some loads are over 50K using a primer designed for a 14.5K max cartridge. The small vent liners restrict the gas pressure enough so it's not an issue until the hole erodes. On cartridges with low pressure it's possible the primer pressure is greater than the chamber pressure.

I don't ever remember seeing what pressures just a primer would produce in the cup and pocket.

Different relative strengths of primers here:

http://www.castingstuff.com/primer_testing_reference.htm

http://www.jamescalhoon.com/primers_and_pressure.php

[Bloodman14]

What is a vent liner? Not owning a smokeless muzzle loader, the term is beyond me. Not questioning your wisdom or experience, sir, just looking for some education.

[Larry Gibson]

"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.

238389

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. The point of this test was to determine that. It is not suggested what so ever that full power loads be developed and used with cases having drilled out flash holes.

Such cases 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.

[M-Tecs]

What is a vent liner? Not owning a smokeless muzzle loader, the term is beyond me. Not questioning your wisdom or experience, sir, just looking for some education.

https://www.badgerridgeind.com/store/p11/LehighVentLiner.html

[M-Tecs]

"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."

I don't know the answer but I tend to agree that it's not an issue at SAAMI pressures. Before the high BC bullets were allowed for Palma competition some would push the limits pretty hard. These people claimed the small flashhole small primer pocket 308 case would withstand the high pressures better. The actions for these loads normally didn't have ejectors since the brass would flow into the plugger hole. Barnard, RPA and Gilkes-Ross are the ones that come to mind.

When the 80 grain Sierra Bullet was the only option for 5.56 long range loads the AMU used a load called the V8. They used virgin primed LC brass with crimped GI primers. The primer pocket was shot after one firing. If I remember correctly the claim was it was about a 77,000 PSI load. Never fired any but I did pick up some of the brass from V8 loads and even with the hard LC brass and crimp GI primer the case pockets loosened to the point they were unusable after the first firing.

Would enlarged flasholes make a difference in this loads? I don't have a clue and the need for these type of loads has long since past due to rule changes and higher BC bullets.

Back to reality. The only cases that I have enlarged the holes on are 38 Spec and 45 Colt for wax bullets and 45/70 rifle for Blackpowder loads. These were mostly for other people. I did try a limited amount of 45/70 with enlarged holes for BPCR but I found no improvement in accuracy. My testing was limited and far from the end word on the subject. I didn't see any advantage and since I segregate my 45/70 into the 3 pressure levels and a fourth for Blackpowder only cases I didn't want to mess with a fifth group for enlarged flash holes unless I saw a real benefit.

All of my ultra low pressure loads have been on rimmed cases shoulder so setback is something I have never had to deal with.

Personally I always believed that the pressure inside the primer cup would be the same based on gas flow dynamics regardless of flashhole size in the case until I started with the smokeless muzzleloaders with 209 primers. In this case the .032 vent liner allows the 209 primer to be used with 50K+ loads. I an not sure why this works since a restriction of this type should not reduce pressure just volume of flow. It may be a simple as the volume of flow is reduced enough that it allows the 209 primer to leak enough that pressure limits are not exceeded. Not sure if I will build anymore but if I do I will switch to the newer designs that use large rifle primers like this: http://arrowheadsporting.com/arrowheadplug_lrmp.html

[mvozz]

WOW, This is why I hang out here and read more than I post. Lots of brain power here making me a bit more enlightened about this new hobby. Thanks Larry!!

[Bloodman14]

https://www.badgerridgeind.com/store/p11/LehighVentLiner.html

So, does that thing thread into the front of the breech plug, with the 209 in the back? Does it act like a flash hole extension?

[M-Tecs]

So, does that thing thread into the front of the breech plug, with the 209 in the back? Does it act like a flash hole extension?

Yes it threads into the front of the breech plug. Other versions use carbide bushings. http://arrowheadsporting.com/breechplugs.html

Not sure what a flash hole extension is but these systems do reduce and extend the flash hole. Once they erode accuracy goes south fast. If you continue primers get sticky. The question is why? I am starting to believe the sticky primers are from increased volume of gasses exceeding the leakage. Not sure why the accuracy goes south so fast.

[Elkins45]

https://www.badgerridgeind.com/store/p11/LehighVentLiner.html

Keepers those are expensive. I think you can buy the Savage ones cheaper.

Even though I don’t shoot my rifle very much every year (two sighters, two deer max) I bought a bag of stainless coned head screws and some .030 bits. I am planning to make my own if I ever use up the factory ones I have.

[edward hogan]

Is drilling-out, enlarging, flash holes "dangerous"?

I dunno... but since I have owned the RCBS broach tool for about 25yrs; I use it.
Seems like a lot of trouble to drill flash holes larger; and it changes one very large variable; namely, the volume of flame entering the case and igniting the powder charge.

To what real purpose? Does it invalidate all the loading manual data? Probably. Loading manual data all works off pressure readings. The flash hole uniform diameter is a very valid pressure constant. Anyway.... what kind of jig would you use to maintain the centering? Sure, there are taper drills and two-step drills; but very spendy and wouldn't you still need your brass mounted in a die or something like a Wilson Trimmer case-holder?

I like the RCBS Flash Hole uniforming tool because the broach uniforms the brass that's extruded into the case from the flash hole drill. Not every case needs uniforming; Lapua is about 100% ready to go, but for uniform ignition in making match quality ammunition, you do it anyway; at least I do.

Certainly drilling out flash holes would be a danger in an over-pressure situation, pierced primer, blown primer. Greater volume of gas venting through your bolt body, about 4" from your eyes???

Uniforming with a broaching tool delivers consistency within the spec used by all companies that publish data. There are, after all, different load data sets for large and small primed case cartridges. Doesn't seem worth the risk to me.

[Larry Gibson]

edward hogan

Is drilling-out, enlarging, flash holes "dangerous"?
I dunno... but since I have owned the RCBS broach tool for about 25yrs; I use it.

To what real purpose?

That is the subject of the question asked in the opening post. The test has shown that it is not, at lest with a 55 - 56,000 psi load using hacketed bullets of 147 - 168 gr. I use a Lyman flash hole uniformer but it does not alleviate the problem that drilling flash holes alleviates; that of case headspace problems associated with reduced loads (squib, cat's sneeze, mouse fart, etc). It is a known. provable fact that drilling the flash holes out larger in cases used with such loads negates the primer from pushing the shoulder back on rimless cases, especially in push feed actions. when inadvertently using such a case with a drilled flash hole presented any problems was the question.

Seems like a lot of trouble to drill flash holes larger; and it changes one very large variable; namely, the volume of flame entering the case and igniting the powder charge.

It's not really a "lot of trouble" as it is easily done with a hand drill or with a drill press. Takes no more time than uniforming the flash holes with a RCBS or Lyman tool. Yes, it does change that one variable that the flame does get into the case quicker filling the case volume better. This has proven beneficial with improved ignition when small charges giving very low load density are use. Internal ballistics are often improved with those loads and powder position sensitivity is also lessoned.

Does it invalidate all the loading manual data? Probably. Loading manual data all works off pressure readings. The flash hole uniform diameter is a very valid pressure constant.

How so would it invalidate loading manual data? Probably not as the test pretty conclusively demonstrates there is little difference between standard flasholes and those drilled out as large as practical. I measured the peak pressure, the time/pressure curves, the rise, the area under the curve etc. and found no evidence of any change between the standard size flash holes and the drilled out flash holes or of any size in between.

Anyway.... what kind of jig would you use to maintain the centering? Sure, there are taper drills and two-step drills; but very spendy and wouldn't you still need your brass mounted in a die or something like a Wilson Trimmer case-holder?

None is needed at all, the cases used above were held in my left hand while I used a small hand drill in my right hand. The existing flash hole is the guide for the drill bit.........was very easy to do.

I like the RCBS Flash Hole uniforming tool because the broach uniforms the brass that's extruded into the case from the flash hole drill. Not every case needs uniforming; Lapua is about 100% ready to go, but for uniform ignition in making match quality ammunition, you do it anyway; at least I do.

Again you miss the point of using cases with the flash holes drilled out. Were not talking "making match quality ammunition" we're talking making squib, cat's sneeze, mouse fart loads.......

Certainly drilling out flash holes would be a danger in an over-pressure situation, pierced primer, blown primer. Greater volume of gas venting through your bolt body, about 4" from your eyes???

Ah yes, one of the usual "fears" expressed.......except the evidence doesn't demonstrate that. By the time you get to a blown primer the size of the usually is eroded out also. You have blown enough primers with various size flash holes with "over pressure loads" in an actual test to have definitive proof? Or is it just conjecture?

Uniforming with a broaching tool delivers consistency within the spec used by all companies that publish data. There are, after all, different load data sets for large and small primed case cartridges.

Again you miss the point. Obviously you don't use squib, cat's sneeze or mouse fart loads because I don't see any in the major loading manuals. Certainly is your choice. If you should change your mind and try some (BTW; drilling the flash holes is only recommended in cases taking LR primers........a closer reading of post #1 would reveal that), especially in rimless cases in a push feed action you may find to your dismay the headspace of your uniformed cases that the headspace has shortened in only a few firings of such a load. When you get misfires and/or failure to extract you'll then, perhaps, understand.

Doesn't seem worth the risk to me.

The reason for the test was to determine if there was a "risk". The test demonstrated there is no "risk". But again, you are entitled to your own opinion.

[M-Tecs]

On the issue of does a drilled out flashhole increase the pressure in the primer? I don't see anyway this could be possible since the duration of maximum pressure in the case and barrel far exceeds the time it would take to equalize pressure in the primer pocket. What could change is the rate of flow but again I don't see how this would have a meaningful effect at SAAMI and under pressures. The other theory is the larger flashhole changes the rate of the powder burn. Larry's test results show this is not a significant factor.

In the case of the why smokeless muzzleloaders running very high pressures can get by with using 209 primers I am not sure. They do use vent liners with .030" holes. I have ran mine you to about .040" and started getting sticky primers. Sticky primer extraction indicates over pressure for this type of system but why? These types of systems have some leakage and the larger hole MAY allow the rate of flow to exceed the rate of leakage??? Could be something else also?????

I have no clue how much pressure a 209 will withstand but based on Tom Roster tests it's a lot more than I would expect . https://www.shotgunlife.com/shotguns/tom-roster/important-information-about-shotshell-pressures.html

[Texas by God]

I received 100 30-30 cases from a member here in which the primer Pockets had been uniformed and the flash holes drilled out larger. I am glad to hear that I can use them with normal loads not just light loads.

Sent from my SAMSUNG-SM-G930A using Tapatalk

[crackers]

Thank you for sharing all that work. I don't often size cases and this seems to be the root of my intermittent low pressure neck joint donuts in 308 and 358.

[swheeler]

Larry good test, I often wondered about the warnings posted of accidentally loading a full pressure load in drilled brass being dangerous. I do find the pressure and velocity of 43 gr IMR 4350 with a 150 gr bullet in the 308 to be higher than I would have expected.

Larry, you never replied to my questioning of the data you posted here, did you make a mistake? 43.0 grs of IMR 4350, 147gr fmj from 24 inch barreled 308, 2800 fps and 56k psi, this just does not sound correct?????

I went out today with 5 rounds of 308 ammo to run over the chrony

Temp was 47*F
308 TC Compass 22" barrel

IMI brass FL sized(heaviest brass I have)
150 Horn SP seated to cann seating depth .322"
CCI#250 Primer

43.0 Gr IMR 4350

2234fps 43 fps extreme spread
If I had to make an educated guess as to pressure 40K

550 fps is a big gap for 2 inches of barrel

[JimB..]

Larry, interesting work, thanks for publishing your results.

“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.”

Is it correct to say that this depends upon the primer backing out? If the primer does not back out then it would exert no net forward pressure on the case, correct? I’m working from 1st year physics that’s several decades old; the question is sincere.

If that’s the case, then would staking (difficult) or sealing (easy) the primers in cases with standard flash holes contribute additional useful data to the analysis? I’d think that such cases would show no increasing headspace, further refuting the firing pin theory and supporting the primer pressure theory.

[Bloodman14]

Jim, I think your question is correct; the primer fires, and sets back against the bolt face, hence driving the case forward (since it cannot expand into the chamber fully), which in turn forces (sets) the shoulder back. Sealing or staking the primers in might work, but with properly sized brass, don't know how worthwhile it would be, unless you are working with new brass that has been FL sized.

[JimB..]

Larry, interesting work, thanks for publishing your results.

“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.”

Is it correct to say that this depends upon the primer backing out? If the primer does not back out then it would exert no net forward pressure on the case, correct? I’m working from 1st year physics that’s several decades old; the question is sincere.

If that’s the case, then would staking (difficult) or sealing (easy) the primers in cases with standard flash holes contribute additional useful data to the analysis? I’d think that such cases would show no increasing headspace, further refuting the firing pin theory and supporting the primer pressure theory.


Jim, I think your question is correct; the primer fires, and sets back against the bolt face, hence driving the case forward (since it cannot expand into the chamber fully), which in turn forces (sets) the shoulder back. Sealing or staking the primers in might work, but with properly sized brass, don't know how worthwhile it would be, unless you are working with new brass that has been FL sized.

When the primer fires the pressure in the primer pocket dislodges the primer and it starts moving back and the case moves forward. The product of ignition is also squirting through the flash hole which also tends to push the primer and case rearward.

Where I have a problem with the idea that the primer firing is causing shoulder setback is that it seems counterintuitive for the primer to show no effects of firing even though it has negligible mass relative to the mass of the rest of the cartridge. I understand that the energy is mass x velocity, so the primer is going to be going rearward at high speed while the rest of the cartridge is poking along until the powder charge fires, at which point the bullet pops and the case moves rearward.

I’m rambling, but the physics of the thing interests me.

What happens if you fire a primer in a case with no bullet? If the primer is moving the case forward, removing the powder and bullet shouldn’t materially change the deformation at the shoulder.

[Larry Gibson]

What happens if you fire a primer in a case with no bullet? If the primer is moving the case forward, removing the powder and bullet shouldn’t materially change the deformation at the shoulder.

But it does as mentioned in the testing conducted and reported in post #1 I believe.

[swheeler]

Larry , I see you finally edited your data to 4895 powder instead of 4350, rookie mistake!;-)

[JimB..]

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.

I’m not sure why, but I had believed that you were using your powder puff loads for this stage of the testing as well as for the next stage where you drilled out the flash holes and fired 50 rounds from each case. Thank you for the clarification.

I’m still curious about what happens if you stake the primer. My expectation is that there will be no setback as there are no material forces pushing the case forward.

[Larry Gibson]

Larry , I see you finally edited your data to 4895 powder instead of 4350, rookie mistake!;-)

Yup, that's me....a rookie for sure......

[swheeler]

Probably just a senior moment, I have mine every so often.

[Larry Gibson]

Additional test also in 44 Magnum and 45 Colt at; http://castboolits.gunloads.com/showthread.php?379607-primer-only-case-locks-up-cylinder/page2

Post #34

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”

With Standard flash holes;
Velocity; 1060 fps (muzzle)
SD/ES; 7/23 fps
Pressure; 16,300 psi(M43)
Pressure SD/ES; 400/1,500 psi
Group; 2.9”

With flash holes drilled;
Velocity; 1059 fps (muzzle)
SD/ES; 4/15 fps
Pressure; 16,000 psi(M43)
Pressure SD/ES; 400/1,100 psi
Group; 3.15”

From the measured data we see there is essentially no difference. Again the sky did not fall, California did not slide off into the Pacific and still no Trump collusion with Russians……

Here’s the fired primers…..no difference in “flattening”…….

240878

Essentially, after thorough testing, there appears to be no detectable "danger" based on the size of the flash hole when using LP or LR primers at low or high pressures.

[Ramguy]

Wow!!! That's a lot of info. I was looking to load some plinking loads in a .45LC with some brass that had enlarged flash holes, and that very question was answered in the very last post!!! Thank you for sharing your knowledge and testing information.
felipe

[megasupermagnum]

If you think about it, percussion cap muzzleloaders use a .028", sometimes smaller orifice to delay blowback to the cap, and that's with blackpowder pressures. The .060"+ flash hole on new brass is already beyond delaying anything.