Flash hole blow up

[mooman76]

Joeb
I thought I answered you but guess not. The chamber vent hole I have only seen a few times in older rifles like late 1800's early 1900's. Mine is a spanish mauser 7x57 of some type from that era. The vent hole is in the chamber or right behind I guess. You can't see the brass case but you can see the front part of the bolt. The hole is figure 8 shaped like the drilled 2 holes together. I was told it was to vent excess pressure rather than blow up the gun. I assume sence you rarely see this and never on a modern rifle, it didn't work or at least didn't always work as intended!
I do have a 7.7 jap but and it is the late production no frills but it has a perfect cusantiminium ( I can't spell the flower)so I'm not willing to blow it up! But this spanish mauser is a piece of C$@p. Let me know what you want to do!

[Bass Ackward]

Right, it's unpredictable as substituting a magnum primer for a standard one in a worked up maximum load is. Start with a sane reduced load and work it up, and you can be safe with it IMO.

Ric,

I dropped 3 full grains which should have been like 45,000 psi and certainly safe enough to substitute a magnum primer in that situation. That's how slow the powder was for that application. And since "all" cases stretched 3/16 " on a single firing, I doubt that any magnum primer change would do that. And realize that 52 grains is to the bottom of the bullet. No SEE, no filler. Nothing else to blame it on.

That is my point. I understand exactly how you feel. I know because I would have bet my place in heaven on situation 2. But .... I found situation 3.

So at least consider the possibility, there is bend in the road ahead and maybe you will recognize it when you come to it.

[Ricochet]

Hmmm. Hard to see how the flash hole size alone could make such a big difference. I'd love to see some pressure test data!

[joeb33050]

Joeb
I thought I answered you but guess not. The chamber vent hole I have only seen a few times in older rifles like late 1800's early 1900's. Mine is a spanish mauser 7x57 of some type from that era. The vent hole is in the chamber or right behind I guess. You can't see the brass case but you can see the front part of the bolt. The hole is figure 8 shaped like the drilled 2 holes together. I was told it was to vent excess pressure rather than blow up the gun. I assume sence you rarely see this and never on a modern rifle, it didn't work or at least didn't always work as intended!
I do have a 7.7 jap but and it is the late production no frills but it has a perfect cusantiminium ( I can't spell the flower)so I'm not willing to blow it up! But this spanish mauser is a piece of C$@p. Let me know what you want to do!

Now I think I understand about the vent hole.
Here's what I think the experiment should look like:
Take 5 once-fired cartridge cases and drill the flash holes out with a 1/8" drill.
Load these with a full power safe (max) load. In the Lyman 48th there are a number of 45,000 CUP loads, none much higher.
Get a tire and a string.
Shoot them and see what happens.
Pictures would be great.
If the gun doesn't blow up or do anything bad, repeat with 5 cases with the flash holes drilled with a #28 drill, .140"

I don't see any point to working up to it, we want to know if the gun blows up with full power loads.

Anybody else chime in about the experiment protocol.
I wish I could be there!!
joe b.

[trk]

If the cards are played right, the gun could (afterwards) be a candiate for the next gun-by-back campaign by the anti-gun folks.

[joeb33050]

Now I think I understand about the vent hole.
Here's what I think the experiment should look like:
Take 5 once-fired cartridge cases and drill the flash holes out with a 1/8" drill.
Load these with a full power safe (max) load. In the Lyman 48th there are a number of 45,000 CUP loads, none much higher.
Get a tire and a string.
Shoot them and see what happens.
Pictures would be great.
If the gun doesn't blow up or do anything bad, repeat with 5 cases with the flash holes drilled with a #28 drill, .140"

I don't see any point to working up to it, we want to know if the gun blows up with full power loads.

Anybody else chime in about the experiment protocol.
I wish I could be there!!
joe b.

And PLEASE, mooman76, write everything down the day and date and load and where and everything. And PLEASE, be careful.
Thanks;
joe b.

[porkchop bob]

IMO, the results will be a wasted rifle and mis-leading results. Two stated variables - vent hole and drilled out primer hole. Will a newbe read the posting and conclude anything less will be safe in his or her rifle? How many times will the test be repeated to rule out the posibility the first rifle was not stronger than usual? What assurances will any of us have our rifle is as strong?
Bob

[Char-Gar]

The only way, at least in my mind, to settle the issue is to have a lab do the test in a pressure gun. How much could it cost to have 15 rounds put through a pressure gun?

[Ricochet]

That would be the only useful data, from measuring pressures with normal and enlarged flash holes. And I'll bet it's been done, if we could find it.

[joeb33050]

This is all about safety, and advice to shooters.
If you don't understand what it's about and why, please read the thread-I think it's pretty clear. If that doesnt clarify the matter, ask and I'll give it a shot.
If you have questions or criticisms or suggestions about the test protocol, please write them here.
We're not interested in measuring anything here, we're/I'm interested in testing the ?hypothesis?: If you shoot a 30/06 at 50,000 pounds pressure with a case with a flash hole enlarged to 1/8", then the gun will blow up."
If the 7MM mauser blows up, we have evidence that the hypothesis is correct.
If it doesn't bl;ow up, we have some evidence that the hypothesis is incorrect.
In neither case is the evidence 100% PROOF-
Ricochet, chargar and porkchop bob-your opinions are always welcome; please make sure to comment after the test, no matter the outcome.
Thanks;
joe b.

[Larry Gibson]

joe b

So then to clarify with the flash hole drilled cases; are you loading (going to test) the 7mm Mauser to normal cast bullet velocity for this cartridge, i.e. a 160-175 gr cast bullet over a medium burning rate powder to 1800-1900 fps? Or are you loading the 7mm Mauser to factory (European) pressures with 139 - 175 gr jacketed bullets to 2800 to 2400 fps respectively?

I ask because I have already snuck up to 2044 fps with the 123 SKS/AK bullets the '06 over 18 gr Unique with well fire formed cases and the flash hole drilled with a #28. Those loads do not exhibit any signs of excessive pressure being applied to the primer. I have shot several hundred of them so far. I also have been working with the .308 with flash holes drilled and 311291 over 4895. I'm up around 1800 fps and again no sign of excessive pressure on the primer.

Larry Gibson

[porkchop bob]

Joe B.
I have read this thread a few times. I will comment, try to summarize and ask questions.

I agree the pressure on both sides of the primer hole is the same.

Now let’s talk about force. Increasing the size of the flash hole will increase the force exerted on the primer side of the flash hole. Assuming the bolt face is even and snug against the primer, the weak point will be the dimple from the strike of the firing pin.

Hopefully, the firing pin, in the test rifle, fully retracts behind the face of the bolt after striking the primer. The test results should make a note of this.

Paint the bold lugs with machine blue and see how tight and evenly they fit when the bolt is closed. Measure them again after the tests, if it is possible.
_ If not tight, the bolt will set back and the brass will flow at the base.
_ If not even, the bolt will cant to one side and the brass will be distorted and flow more so towards that side.

There is only one test rifle.
_ The variable will be a set of rounds loaded in brass having an enlarged primer hole. As I understand it, a load designed to blow the rifle up.

_ Missing is a similar set of rounds loaded in brass having a normal primer hole.

Assuming the rifle does not blow up with the normal set of test rounds, then I would be interested in knowing it did when the enlarged set was fired. I would be more interested in knowing how the case failed.
_ Was it at the primer?
_ Was it at the base of the brass?
_ If not a brass failure, what caused the rifle to blow up?

Joe B., I look forward to the test, published results and findings.

Thanks, Bob

[Ricochet]

I agree the pressure on both sides of the primer hole is the same.

Now let’s talk about force. Increasing the size of the flash hole will increase the force exerted on the primer side of the flash hole.

No, it won't. If the pressure is the same on both sides of the flash hole, so is the force against the primer cup. Force = pressure x area.

The only way this can make a difference is by affecting the pressure developed in the powder chamber, by affecting the ignition of the powder.

The main way I think increasing the size of the flash hole may increase pressure is by letting more of a shock wave from the primer explosion through into the powder, shattering grains into small, uncoated fragments that burn faster. A small flash hole "throttles" the flow of gas from the explosion in the primer pocket, so it's less of a shock mechanically to the powder grains.

Remember, lead styphnate and tetracene are high explosives, as is PETN, which is a major ingredient in some primers. (As also is the diazodinitrophenol found in no-lead primers.) Primers go off with a pretty sharp blast.

[joeb33050]

joe b

So then to clarify with the flash hole drilled cases; are you loading (going to test) the 7mm Mauser to normal cast bullet velocity for this cartridge, i.e. a 160-175 gr cast bullet over a medium burning rate powder to 1800-1900 fps? Or are you loading the 7mm Mauser to factory (European) pressures with 139 - 175 gr jacketed bullets to 2800 to 2400 fps respectively?

I ask because I have already snuck up to 2044 fps with the 123 SKS/AK bullets the '06 over 18 gr Unique with well fire formed cases and the flash hole drilled with a #28. Those loads do not exhibit any signs of excessive pressure being applied to the primer. I have shot several hundred of them so far. I also have been working with the .308 with flash holes drilled and 311291 over 4895. I'm up around 1800 fps and again no sign of excessive pressure on the primer.

Larry Gibson

Larry;
The object is to test a load that produces pressure in the 45,000 pound range as given in the Lyman or other handbook. This is the "full load", max in my manuals-maybe because of the Rolling Blocks?? or earlier Mausers?
I am interested in both of your loads, precisely described, and the guns used. I'd like to know the "Quickload" pressure estimates fot them. If you'll post them, maybe we can find a Quickload owner to run the pressure.
I'd also like to get Bass's load, precisely, for Quickload pressure estimation.

[joeb33050]

Joe B.
I have read this thread a few times. I will comment, try to summarize and ask questions.

I agree the pressure on both sides of the primer hole is the same.
(I don't know what this means.)

Now let’s talk about force. Increasing the size of the flash hole will increase the force exerted on the primer side of the flash hole.
( I don't know that this is true, and suggest that it is not. The primer goes off, blowing flame through an ,080" flash hole. There's some pressure inside the primer/primer pocket cylindrical space with the only opening the flash hole. I don't know what the pressure is, but I do know that the pressure is enough to generate a force that moves the shoulder back on a 30/06 empty case. Now the powder lights up, certainly a continuous thing going on, primer-powder-bullet moves... The pressure builds in the case to ??above ?? the pressure of the primer. ??The gas goes through the .080" flash hole increasing the pressure in the primer slash to ?? but you're suggesting less than full pressure, before the pressure goes down. In my mind I don't see a lot of gas needed going through the flash hole to pressurize the primer pocket. A large primer pocket is .210" diameter X .132" deep with a volume of .0046 cubic inches less the primer and anvil volumes. The ratio of .080" flash hole area to primer pocket volume is ~1:1, 1 square inch to 1 cubic inch, one square foot to one cubic foot. I think about a cubic foot box with one side open and 50,000 psi on the open side, and I see the box fill quick. But, I don't know. I'm thinking that the flash hole, .080" or .125" or .140" is large enough to allow pressure to maximize in the pocket. But I don't know. I don't think that a larger flash hole will increase pressure. BUT, I can see that if the primer fails, then a larger flash hole MAY?? allow more gas to escape, maybe."

Assuming the bolt face is even and snug against the primer, the weak point will be the dimple from the strike of the firing pin.
( I don't know this. If the brass primer cup dimple doesn't flatten back out or extrude into the firing pin hole, and mine don't-this I always took as a sign of excess pressure or bad firing pin/hole geometry- and if the pressure isn't greater in the primer pocket with a big flash hole, then I don't know what's going to fail. I don't know.)
,
Hopefully, the firing pin, in the test rifle, fully retracts behind the face of the bolt after striking the primer. The test results should make a note of this.

Paint the bold lugs with machine blue and see how tight and evenly they fit when the bolt is closed. Measure them again after the tests, if it is possible.
_ If not tight, the bolt will set back and the brass will flow at the base.
_ If not even, the bolt will cant to one side and the brass will be distorted and flow more so towards that side.

There is only one test rifle.
_ The variable will be a set of rounds loaded in brass having an enlarged primer hole. As I understand it, a load designed to blow the rifle up.

_ Missing is a similar set of rounds loaded in brass having a normal primer hole.
( YES, we need to shoot the gun with ~5 rounds and a normal flash hole to make sure it doesn't blow up. MOOMAN, will you add this as the first step?? Thanks!!!!)

Assuming the rifle does not blow up with the normal set of test rounds, then I would be interested in knowing it did when the enlarged set was fired. I would be more interested in knowing how the case failed.
_ Was it at the primer?
_ Was it at the base of the brass?
_ If not a brass failure, what caused the rifle to blow up?

Joe B., I look forward to the test, published results and findings.

Thanks, Bob

Thanks, I needed that!
joe b.

[porkchop bob]

Good evening, Joe B. A Merry Christmas Eve it is.

To address some of the questions you raise.

Think of a long thin balloon and then squeeze it with you hand until you have two sections: a small one and a much larger one. The pressure in both sections will be the same. Picture now a cartridge with the primer pocket/primer being the small section and the larger section being what we think of the inside/volume of the cartridge. Because they are connected by the primer hole, the pressure on both sides will be equal. For an instant, an in-balance can exist, but the pressure will become equal very quickly.

Simple hydraulics says a piston of 2 inches diameter connected to another piston of 6 inches in diameter can multiple the force applied by the smaller piston upon the larger one by a factor of 9. Push the small piston down 9 inches with a one pound weight and the larger one will rise 1 inch with a nine pound weight. (6 is 3 times larger than 2. 3 squared is 9)

In the case of the cartridge and the primer pocket/primer, reverse the situation. Increasing the diameter of the primer hole will result in more force being applied outward pushing the inside of the primer towards the face of the bolt.

There are several engineers on the board. I trust they will comment one way or another on the validity of this simplistic explanation.

Bob

[leftiye]

You're goin' ta have some trouble with primers that won't fire if ya bore out the flash hole until the anvil isn't sittin' on somethin'. Also, though the ignition should be speeded up, there will be a definite place where a larger hole has no further effect.

[Linstrum]

And then to complicate things there are Berdan primers with TWO flash holes! Yeah, I know the holes in Berdan pockets are smaller, but the flame front is initiated in two places.

[Ricochet]

Bob, none of that fancy hydraulic piston stuff applies to this case. What you've got is a pressure in a chamber, and an area of the primer cup that it works against. There's your force. If increasing the flash hole size increases it, it has to be by increasing the pressure in the powder chamber, which connects to the primer pocket. That would have to be by affecting the ignition.

[porkchop bob]

Bob, none of that fancy hydraulic piston stuff applies to this case. . . .

Thanks. This forum is full of lessons to be learned. Bob