exact mode of explosion caused by a short throw

[Magnum Wheel Man]

I personally don't like very small charges with alot of empty case capacity... I've been doing alot of "pop gun" loads using Trailboss... I'm not sure about using it in a semi... but of the 3-4 cartridges I'm loadng with it right now, none of my cartridge loadings are excessive even with the case clear full ( never compress load Trailboss )... I have some light loads in 32 S&W ( 0.7 grains of powder & a lead round ball ) that easily & consistantly shoot sub 2" groups at between 20 & 30 ft... these loads litterally have no recoil, & are as loud as the old time kids cap guns... Trailboss is extremely bulky, & a reasonably fast burning powder... & works great for reduced loads

[Jim Watson]

P.O. Ackley was pretty well convinced that a greatly reduced charge of slow burning powder in a low expansion ratio (strongly bottlenecked) cartridge could give damaging or destructive overpressures. I think his example was a .250 Magnum with about a 70% charge of what we now know as 4831. He didn't come up with a theoretical mechanism for it, but had the broken guns to show.

I really doubt that a very light load of fast burning pistol powder is going to wreck a revolver shooting wadcutters, though.

It would be instructive to clamp a gun you could spare in a rest and shoot successively reduced loads of W296.

A PhD friend said the detonation phenomenon would be a great university research project. Just think how many loads a low-paid graduate assistant could fire in a semester. Enough for some real statistics.

[Unclenick]

I like that idea. I can see the headline: Grad Student Enjoys Thesis Work; Joins NRA and is Shunned By University.

Originally Posted by Braindg

I need to add in here that smokeless powder cannot detonate.

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.

[Jim Watson]

Hatcher said that one known actor in the demolition of "low number" Springfields was the Guard Cartridge, loaded with 9 grains of Bullseye and the 150 grain service bullet. He thought it was the rapid pressure rise of the pistol powder that blew the case head and broke up the overhardened steel.

Of course a .30-06 would hold 18, 27, or maybe even 36 grains of Bullseye if the arsenal crew wasn't careful. The only gun I know to have been demolished on our range was almost certainly a double charge of Bullseye in a .357 magnum. Not a wadcutter, but a misplaced notion of a top Bullseye load for magnum power.

I recall reading that Cordite was used for demolition charges. Of course Cordite contains a lot of nitroglycerine - over half in the original, nearly half in Cordite MD (MoDified.) There is a rural legend hereabouts that some of the good old boys put a blasting cap in a can of Bullseye (30% NG) and got it to go high order, pulverizing the tree stump the can was on.

[Edward429451]

the detonation phenomenon would be a great university research project

They did it. Thier conclusions held that most of the 38's that KB'd had been found to be in the prescense of a Glock at some point beforehand...

[totaldla]

I'd have to read Hatcher's accounts of the 9gr of Bullseye busting a springfield. Thats a tad hotter than what folks use for a plinking load, but it is hard for me to believe that it hits 90Kpsi. This is a case where a double-charge is suspect, as I can believe 18gr of Bullseye could achieve some serious pressure. But I've never read the account from Hatcher's writings, so I don't know how he investigated it.

UncleNick - very interesting. The key of course isn't so much the pressure, but the rate of pressure change. When you exceed the propogation velocity in steel, the steel will "Big Hunk Bar", i.e. fracture. So I can see how a "minor" detonation event could produce a crack, which later blows wide open.

All fun stuff to think about. I love to make 30-30 plinkers using 7gr of Clays and a 165gr cast bullet - about 1100fps and very accurate.

[wncchester]

"I have never heard of H110/W296 causing anything other than squibs. As I said in the beginning, I believe detonation is a myth, a gun-forum old-wives tale, that makes its rounds periodically."

Maybe it depends on what you call a "detonation." In a manner of speaking, any time we fire a firearm is a detonantion, we just usually keep it under control. ??

Check your loading manual's data for H110/W296, you will find the starting and max loads to be very close together. There's a reason for that; don't load that powder down.

[totaldla]

Originally Posted by wncchester

Maybe it depends on what you call a "detonation." In a manner of speaking, any time we fire a firearm is a detonantion, we just usually keep it under control. ??

Check your loading manual's data for H110/W296, you will find the starting and max loads to be very close together. There's a reason for that; don't load that powder down.
Today 04:33 PM

Detonation is a very specific term and our firearms don't detonate. I think the term for what we do is deflagration.

The only reason for not downloading H110/W296 is that when very cold, with loose crimp, there may not be enough pressure to burn the powder - hence a squib. The squib can either tie up the revolver or lodge a bullet in the barrel. I would imagine that a 300gr bullet lodged in the barrel of a 44 mag would cause a blowup if the next round were fired into it. I don't think you'd get away with a bulged barrel.

[Unclenick]

I didn't know the Bullseye Surprise study was done by grad students, but it is limited to the pistol cartridge case where a double charge is disastrous. It doesn't explain detonation in the big capacity rifle cases by small charges of which multiple overcharges would be required just to get to normal pressures. Even with the '06 example, a double charge of Bullseye only makes it to 40 KPSI in QuickLOAD under the 152 grain military FMJ. You need a triple charge to go over SAAMI maximum, and while that's over-pressure, it is still within blue pill pressures, so it still shouldn't blow up the gun until you overcharge 4X. So, some funny business remains to be studied and explained definitively, which is what I would like to see grad students work on.

All combustion occurs when a source of energy puts enough into the combustible material to exceed the threshold at which it releases its stored potential energy by rearranging its atoms into new molecules. Detonation occurs when a shock wave is used to put that energy in, while deflagration occurs when the heat of a flame front does it. Both are forms of combustion or burning.

One simple definition that distinguishes detonation and deflagration is that because the shock wave is a compression wave it increases the density of the explosive material at its leading edge, increasing the speed of sound in the material it is traveling through. Thus, detonation is always burning at above the normal speed of sound in the material, while deflagration always occurs at below the speed of sound in the material. That is because deflagration depends on the rate of heat penetration of the material, which, is normally a slower mechanism. There are some weird exceptions, like focusing high intensity lasers on surfaces, but we don't do that in guns.