20th Century Myths

Date: Fri, 21 Mar 1997 11:35:36 -0600
From: "David A. Tomlinson" 
Subject: 20th Century Myths

Myth 1. "Stored cartridges can kill firemen when they are exploding in a fire."

Wrong.

Please understand that wood burns, and smokeless powder deflagrates. Burning is the combining of the fuel with oxygen; deflagration is the deconstruction of the smokeless powder molecule into smaller gas molecules without any oxygen from the air being required for the process.

The smokeless powder in modern cartridges requires heavy-wall containment to build the high pressure needed to push the bullet at high speed. In a firearm, the primer starts the deflagration (not detonation!) of the powder, and pressure begins to rise. As the pressure rises, the speed of deflagration increases, increasing the rate of rise in pressure, and again increasing the rate of deflagration.

This is a very high-speed process.

Loose smokeless powder, ignited with a match, "burns" (it is actually deflagrating) slowly, making a mild hissing noise. No pressure is generated, because there is nothing to hold the gasses in place -- they just depart into the atmosphere. Without pressure, there is nothing to speed up the deflagartion process -- so the deflagration proceeds slowly, and the only danger a bystander is in comes from the possibility that he may stick part of his anatomy into the "fire."

The only fatality that I am aware of from a smokeless powder "fire" occurred many years ago, and is recorded in "Hatcher's Notebook," an old but very valuable reference book for firearms aficionados.

X, an avid shooter, had collected several hundred pounds of military surplus smokeless powder, which was stacked in his basement handloading room.

He tried a cartridge, newly made, in a rifle -- and accidentally fired it into the stacked powder cans. As the bullet was slowed in passing through the powder grains, it heated the grains and one ignited.

That can of powder deflagrated, heating other cans and starting their deflagration. Each can ruptured as soon as the internal pressure exceeded the holding strength of a tin can -- but that brief containment was enough to accelerate the rate of deflagration a little. There was no explosion -- but that much powder deflagrating inside a room is enough to fill the room with very hot gasses. The shooter died where he stood from inhaling very hot gasses.

So: What happens when a cartridge explodes OUTSIDE a firearm?

Hatcher took a cartridge, and hung it from a small gallows made of wire. Then he put a candle under the primer, and lit it. Then he put an ordinary cardboard box, upside down, over the arrangement.

Once the candle had heated the primer enough, the primer went off and blew itself backward out of the cartridge case. (Yes, a primer will "back out" -- all the way, if not supported by a breech face!). The powder, ignited by the primer, began to deflagrate and the pressure began to rise.

When the pressure exceeded the strength of the brass cartridge case, it ruptured. That put an end to pressure rise and therefore an end to increases in rate of deflagration. The remaining powder deflagrated as if it was a loose pile of powder standing in the atmosphere.

None of the pieces -- the primer, the bullet or any part of the ruptured cartridge case -- had enough energy to penetrate the top or walls of the cardboard box. That was true for every type of cartridge that he tried -- and he tried enough to make certain that it was true for all brass-cased cartridges from .22 rimfire to elephant gun sizes.

To the best of my knowledge, no one has tried Hatcher's experiment with steel-cased military ammunition -- but there is no reason to believe that it would act very differently. The steel case might hold a little more pressure in -- but only to the point where the bullet pops out -- and after the bullet pops out, you are right back to slow deflagration.

Dave Tomlinson, NFA

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