Originally Posted by
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.
(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