I like that idea. I can see the headline: Grad Student Enjoys Thesis Work; Joins NRA and is Shunned By University.
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Originally Posted by Braindg
I need to add in here that smokeless powder cannot detonate.
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Actually there are two conditions under which it can (it is comprised of high explosive(s) after all). One is when the mass gets extremely large it can carry a shock wave like a fluid. But this requires quantities measured in tons, IIRC, and a strong detonator (a stick of high nitro dynamite, for example). Neither of those conditions occur inside a small arm.
The other has shown up in military improvised munitions manuals, and that is when one of several methods are employed to covert the powder form to a gel or solid that has no grain divisions to break up a propagating shock wave. That is why I suggested the powder needs to fuse before detonation can occur. Fusing is commonly observed in squib loads that have extinguished. (One fellow on another board had a good picture of a whole case full of fused 4831 that had been fired and extinguished trying to push a far-too-light bullet down the tube, but I can't locate a link at the moment.)
Totalda,
You are correct the pressures cannot burst a gun once the gas has distributed throughout the case. 3.1 grains of N320 would normally produce about 4,500 psi behind a 170 grain lead bullet in the .308, and can do almost twice that if the bullet is welded in place and can't move. Neither is a threat to a gun with normal integrity.
If you fuse that 3.1 grains (0.2 gm) of powder, you get a density of about 1.6 gm/cc. If you convert the energy density of fused N320 (a little over 6600 joules/cm³ from QuickLOAD's database), to pressure, you get almost 960,000 psi in that same volume. That means you would get a detonating wave front at something like that order of magnitude of pressure running through the explosive mass. That's enough to initiate a crack site in steel. Where a .308 rifle would not normally be bothered by the sudden appearance of 9,000 psi, one with a crack will. The pressure can then tear it open starting from the crack, giving the appearance of a normal overpressure event with no shattering for most of the length of the tear.
Typical detonation claims don't have enough detail to deduce those details. But a barrel burst event I investigated for a firearms manufacturer a few years ago revealed a distinct starting crack whose location was marked by gas cutting over its inside edges. Unfortunately, that gas cutting would be perfectly capable of covering up local edge shattering done by a small detonating charge. (In that case it was not detonation but an obstruction that initiated the burst, and the gas cutting was the length of the obstruction. This happened only at magnum revolver pressure, but it peeled the whole barrel open behind the gas cutting mark where the crack started, including splitting the frame open where the barrel screwed in. I doubt there was a lot of pressure present through much of that splitting because of the gas escaping as the split opened. It's just that once you start a crack or split, you need much lower pressure for the damage to spread.)
I am open to alternative explanation for how 3.1 grains of N320 or even a double-charge of 6.2 grains would be able to break a .308? It won't be because of the direct chamber pressure, though, that's for sure. Creating pressure faster than the evolved gas can expand away from its burning source, thus to have enough peak pressure start a crack, is the only mechanism I have come up with so far, and detonation (supersonic in the explosive medium by definition) is the only way I am aware of to burn an explosive that fast.