Enlarged Flash Hole Diameter

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BudHyett posted this 2 weeks ago

Bud wrote: "I have told my son and two close friends of this to assure after my passing that these W-W cases are separated. This was with the admonishment that enlarged flash holes raise pressure."

Bud,

Have you ever seen an actual test reported that showed that enlarged flash holes raise pressure?  I have heard this conventional wisdom forever but have never heard of any proof.  I know it's a reasonable theory just like a perfect 11 degree crown is needed but -------? 

I don't want to hi-jack this thread.  Maybe start another thread with a warning and a reference to proof.  If this is actually true all CB shooters should know about the danger. On the other hand if there is nothing to it except a long life of being repeated we should know that too.

Possibly in Hatcher's Notebook, or another serious research book of that era, there was discussion of the development of the .30 US Army (.30-40 Krag) and pressures. 

The .45-70 cartridge as a black powder loading was developed with a larger flash hole, .096 if I remember correctly, and initial work on the new .30 US Army used the same flash hole size. Pressure rapidly escalated with nitrocellulose powders and a way to control the back pressure on the primer cup and subsequently pressing the firing pin was desired. There was a combination of factors, 1) the powder must be stable from freezing Arctic to hot jungle climates, 2) the powder must be stable over long storage times,  3) the powder must not overheat and raise pressures in a hot chamber during rapid firing, and the primers must function in these same conditions. This lead to the mercuric primer used until the mid-fifties.  

Also during this time the Ordnance men worked with flash hole size. The physical chemistry characteristics of the ignition pushing back the primer to the bolt face and exerted pressure on the firing pin area was studied. One choice was to shrink the hole size. Testing showed that the .080 flash hole worked best in testing for the above criteria. Larger meant more gas push back spreading pressure to the bolt face and smaller meant less uniform ignition. As with many things in life, the hole size was a compromise. 

That's what I read in Hatcher's Notebook, I believe. There are also several books on producing ammunition that I read at that time which my friends had and I am not sure where were the articles on development of the .30 US Army. Post-divorce, I did not have the money to waste on a television and spent evenings reading firearms books. 

My son and I both own Trapdoors with their weak actions. I shoot black powder cast bullet loads in my Sharps and Rolling Blocks, thus I use W-W brass with enlarged flash holes to assure only these loads can go in the Trapdoor.

I've been around several guns blown up at the range and do not desire this happening to me. Sticky cases on the hot Midwest summer days of my youth is as far as I want to go.

I can't state from my own experiments that this is true, I only know what I've read of other's experiments. 

  

Country boy from Western Illinois, living in the Magical Pacific Northwest

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Redleged posted this 2 weeks ago

Hi,

Larry Gibson did some fine research and testing on this and found no increase in pressure / danger when the primer holes were enlarged.

Ed

Drilled-Flash-Hole-Test-44-Magnum-and-45-Colt

Is-drilling-out-flash-holes-dangerous-in-a-.308W?

 

Growing old is mandatory, growing up, however, is totally optional!

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cfp4570 posted this 2 weeks ago

Interesting reading. A few years back I was sorting through a bucket of brass picked up at an indoor range and found a bunch of Winchester lead free .45 acp cases and noticed they had very large flash holes. I was a little hesitant to reload them but did anyway with the same load I was using at the time and shot all of them and noticed nothing unusual so I mixed them I with the rest of my brass.

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John Carlson posted this 2 weeks ago

I also did some testing with enlarged flash holes in 30-06 cases fired in several 03A3 Springfields.  While I had no pressure measuring equipment I did fire the test rounds over a chronograph.  I found no significant variations in velocity or accuracy.  It did however show a reduction (practically an elimination) of protruding primers after firing. My results were published in the May/June 2019 Fouling Shot #259.

Holding public office should be viewed as an obligation to serve, not an opportunity to rule.

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RicinYakima posted this 2 weeks ago

I have accidently loaded jacketed bullets hunting loads in 20 cases that I had enlarged the primer hole. My high school physics tells me that gas pressure is equal everywhere in a closed system. However about half the primers cracked between the face and the sides where the curve is at. My thought is that the volume of gas at full pressure is overwhelming the mechanical strength of the unsupported primer edge and cracking them. That lets gas leak back onto the bolt face. FWIW

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beltfed posted this 2 weeks ago

Drilling out flash holes was a practice for prepping 30-06 cases

for reduced cast bullet loads. Reduced the backing out of primers

upon firing the lower pressure loads, OF COURSE I marked these cases

so I would not accidentally load them for full jacketed hunting or target loads....

beltfed/arnie

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John Alexander posted this 2 weeks ago

This topic is sounding more and more like one that could use some additional testing to see if John Carlson's or Ric's experiments can be replicated or to try to replicate some  other studies that found, or didn't find, problems (Sharps,or whatever). 

After all, if it really is dangerous we should know under what conditions.  How big is too big, etc. and make sure we warn shooters. And if it isn't stop misleading them.

I have smoked and blown out primers (none in the last 50 years) but I have never seen one crack.  Is this common in accidently too high pressure loads?

Ric's high school teacher is correct the pressure is equal in all directions everywhere in a closed chamber but only when in a static condition.  But in a cartridge being fires we have far from a static condition and we have two chambers connected by a flash hole, not one.  First the primer goes off and hot gassed shoot out one way, then the chamber increases rapidly to perhaps higher pressure and gases maybe shoot back through the flash hole to equalize the pressure and the normal sized flash hole restricts this flow enough enough that the pressure in the primer chamber never gets up to peak chamber pressure.  In fact something like this must happen if there is anything at all to oversized flash holes causing trouble because oversized flash holes can't produce more pressure than peak chamber pressure. 

If the normal size flash hole doesn't restrict flow enough to keep the pressure inside the primer chamber below peak chamber pressure pressure then we would always have peak chamber pressure in the primer chamber and enlarging the flash hole couldn't increase it.

Having the size of the flash hole small enough to restrict gas flow and keep the pressure in the primer chamber below peak chamber pressure seems like a pretty dubious, but conceivable, theory but one that has to be correct if oversize flash holes are the cause of blown primers and worse.  I'm sure the people at Federal know if this is true or not.  What do they say?

John

 

 

 

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TRKakaCatWhisperer posted this 2 weeks ago

this is a fragment of the article in the Complete Guide to Handloading by Philip B. Sharp  pg 35  Note the increase of velocity and the dangerous increase of pressure.

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Redleged posted this 2 weeks ago

This topic is sounding more and more like one that could use some additional testing to see if John Carlson's or Ric's experiments can be replicated or to try to replicate some  other studies that found, or didn't find, problems (Sharps,or whatever). 

After all, if it really is dangerous we should know under what conditions.  How big is too big, etc. and make sure we warn shooters. And if it isn't stop misleading them.

John

Hi John and all,

The purpose of my previous post wasn't to stir the pot about the "danger" of enlarged flash holes, rather to offer some testing data to BudHyett's post. It seems there are two camps...those who think it's dangerous and those who do not. If further testing is to be done, who is to do it? Who else here (besides Larry) has test barrels and a pressure gauge to empiracally measure pressure at the chamber? I know most of us have chronographs, but that's only part of the analysis. Putting a snippet of a 70 year old reloading manual doesn't satisfy my need for objective proof as there is no mention of precisely what was tested. What were the conditions, and were these already at max or over-max loads?  I also don't doubt that Ric had some primers crack, but that was one incident that may, or may not have been related to enlarged flash holes. I'm wondering if all of you actually read Larry's thread on the effect of enlarged flash holes in a .308? It seems like he's got all the data there, from a control group with no alteration, to incrementally enlarged flash holes all the way up to 0.140". Each having velocity and pressure data to accompany the test firings. There was also another test done by a graduate student as his Master's Thesis supported by ammo manufacturer Fiocchi. Interestingly, he found a slightly higher pressure with smaller flash holes, and increased precision with an enlarged flash hole.

Like I said, it wasn't my intent to stir the pot. For those who firmly believe it's a dangerous practice, don't do it. As for myself, I'm not concerned enough about it to worry and Larry's data seem to support that.

Ed

Growing old is mandatory, growing up, however, is totally optional!

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RicinYakima posted this 2 weeks ago

Ed, Not disagreeing, nothing is dangerous until it is, like flying on a 737MAX. My comment was just my experience that could have been faulty primers? excess resizing of case to create increased headspace? It concerned me enough that I don't do the enlarged flash holes anymore. Ric

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Larry Gibson posted this 2 weeks ago

 

Faulty primers or faulty anything else will fail regardless.  The size of the flash hole has nothing to do with other failures.  If you read the results of the extensive test I did (especially the first one below) which were conducted with high pressures in the 308W you will see the size of the flash hole does not effect pressure.  Nor was there any evidence that pressure increased in the primer. 

I have Sharpe's book and have read it extensively over the years.  I have found several things he mentions that I have been unable to support with extensive testing.  The above posted quote from his book about the size of flash holes is one of them.  Besides the tests with the 308W, 44 magnum and the 45 Colt I have also run comparative test with drilled out flash holes (#28 drill....the largest that should be used with LR primers) in the 30-06, 8x57, 375 H&H and the 45-70 with both cast and jacketed loads involving standard pressures upwards of 60,000 psi.  No increase in pressure was measured with the flash holes drilled out and no indication of increased pressure in the primer was observed.  Additionally I have pressure tested several different milsurp cartridges [7.65 Argentine, 7.62x54R, 8x57] that were converted from Berdan to boxer primers.  Those have the new central flash hole for the boxer primer plus the original one or 2 flash holes for the Berdan primer.  Again, no increase in pressures was measured with top end cast and jacketed bullet loads. 

Further pressure testing in the 44 magnum and the 45 Colt demonstrated the same.

 

http://castboolits.gunloads.com/showthread.php?377629-Is-drilling-out-flash-holes-dangerous

 

http://castboolits.gunloads.com/showthread.php?381156-Drilled-Flash-Hole-Test-44-Magnum-and-45-Colt

LMG

 

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

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John Alexander posted this 2 weeks ago

I urge everybody with the slightest doubt about Larry's test results read the more complete report posted to boolits and referenced at the bottom of his post.

=========

Larry,

Thanks for slaying this zombie. It has been running amok in the population spreading terror long enough. 

Of course it won't stay dead.  And for some shooters your comprehensive work won't even make the zombie sick because they have been told the opposite or worse yet have seen it in print somewhere.

But for me, and I think for most shooters with open minds -- that zombie is dead. And it should stay dead until somebody repeats your tests with modern equipment, powders, and primers and finds different results.

I hope you will submit the test report you posted on Boolits to Glenn for possible publication in the Fouling Shot so it will have wider readership.  Cast bullet shooters have so little experimental work of that caliber to correct all the myths floating around that it shouldn't be hidden away in a couple of online forums.

John

 

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RicinYakima posted this 2 weeks ago

 Well, I read all the thread links above and took a nap to think about all of this stuff. It sort of leads me back to my reloading practices. Other than hunting ammo, almost all of my 30/06 loads use 16 grains of A2400, 150 grain to 220 grain bullets. In the '03, the head space is increased with every firing until the extractor will no longer let the case go forward. So when I loaded these modified cases with most likely 200 grain Speers over 55 grains of H4831, the primers could have backed out. Then the case slide back and pinched the sides? At least we know now it wasn't pressure.

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45 2.1 posted this 2 weeks ago

 So when I loaded these modified cases with most likely 200 grain Speers over 55 grains of H4831, the primers could have backed out. Then the case slide back and pinched the sides? At least we know now it wasn't pressure.

That thin primer cup is a poor substitute for the cartridge case brass around it.

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Squid Boy posted this 2 weeks ago

Another interesting topic and here I am wondering about the powder being used with these enlarged flash holes and if the powder can infiltrate the primer and possibly upset the characteristics of the ignition sequence. Shotgun primers have a thin membrane over the flash hole for this very reason. I have replaced Berdan primers with 209 shotgun primers in 577-450 cases and haven't seen any difference with the same load as a Boxer primed case. Just something to think about. Thanks, Squid Boy

"Squid Pro Quo"

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JimmyDee posted this 2 weeks ago

There are, I think, two big differences in the cartridges discussed here that need more emphasis: (1) straight wall vs bottleneck cases and (2) typical pressures encountered in cast vs jacketed bullets.

I'm not exactly sure what differences the case shape make but all the throat-burners are overbore bottleneck cartridges.  Knowing that gas temperature and pressure are linearly co-related, to me, that infers that bottleneck cartridges operate at higher pressures.  And, of course, we all know that cast projectiles run at substantially lower pressures than commercial jacketed bullets.

Give these two points, it would be foolish to apply anecdotal "I had no problem" experience with straight-wall pistol cases to any bottleneck case which might be used with jacketed bullets.

Bud is, I think, wise to warn others not to use them.

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JimmyDee posted this 2 weeks ago

the size of the flash hole does not effect pressure.  Nor was there any evidence that pressure increased in the primer. 

Do you have any idea what could account for what Sharpe reported?

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Ken Campbell Iowa posted this 2 weeks ago

...i memorized Sharpe's book in the 7th grade ...inspirational to a young farmboy who liked to blow stuff up ... but about 6 years later i learnt that nobody ever gets everything right ...

on another slice of the pineapple, , some pretty good mj benchresters have told me that they fine-tune a load by varying the flash hole ... maybe they done seen that farm boy in me ... ? ...

ken

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TRKakaCatWhisperer posted this 2 weeks ago

the size of the flash hole does not effect pressure.  Nor was there any evidence that pressure increased in the primer. 

Do you have any idea what could account for what Sharpe reported?


 

His test was simple - one loading with regular flash-hole size and one with enlarged.  Easy enough to replicate the test. 

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Larry Gibson posted this 2 weeks ago

CBA Member

 

JimmyDee posted this 9 hours ago

 

the size of the flash hole does not effect pressure.  Nor was there any evidence that pressure increased in the primer. 

Do you have any idea what could account for what Sharpe reported?

No, unfortunately Sharpe gives little detail as to the cartridge, number of rounds tested, components used or if the tests were conducted at the same time.  Especially not known are the primers used.  primers we use today are different than the primers used back then.  Just to many variables left to our imagination to make a guess.

LMG

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

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Larry Gibson posted this 2 weeks ago

CBA Member

 

Ken Campbell Iowa posted this 5 hours ago

 

...i memorized Sharpe's book in the 7th grade ...inspirational to a young farmboy who liked to blow stuff up ... but about 6 years later i learnt that nobody ever gets everything right ...

on another slice of the pineapple, , some pretty good mj benchresters have told me that they fine-tune a load by varying the flash hole ... maybe they done seen that farm boy in me ... ? ...

ken

ken

Maybe something to that.  If you look at the accuracy results when I switched to the 168 MK bullet the accuracy got better as the flash hole got larger.  The last three sub moa groups is the best that barrel has done.  

LMG

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

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Squid Boy posted this 1 weeks ago

I just wanted to interject one more thought on this subject. It would seem from the posts that accuracy does in fact improve as the flash hole is opened but what accounts for that? My guess here is that with a small hole, a considerable amount of pressure is built up inside the primer pocket and as a result the jet of flame is very hot and very strong maybe going deep into the case and flinging the powder around. The more open hole tames this violence down somewhat and possibly creates a more regular burn condition. My understanding of match grade primers is that they are not quite as powerful as standard but also much more exacting in their ignition characteristics. Of course I could be completely off the mark here but I am wondering at these results enough that I plan to try it myself. Thanks, Squid Boy

"Squid Pro Quo"

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