Is drilling out flash holes dangerous?

[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.


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[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/...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.