Occasionally a story appears in a newspaper describing how fire fighters fought a blaze in a sporting goods store as bullets from exploding ammunition "whizzed by" and cans of gunpowder "exploded" around them. Although this type of story makes fine newspaper copy, it bears no relation to what actually happens in a fire involving ammunition and gunpowder.
Smokeless powder is used in all modern cartridges. When it is ignited in a gun, heat, and gas are produced, both of which are confined initially to the chamber. As the pressure of the gas builds up, the chemical processes of combustion are speeded up so that the rate of burning becomes relatively instantaneous, and an "explosion" is produced. This explosion, however, occurs only when smokeless powder is ignited in a confined space such as the chamber of a gun. Outside of a gun, the powder will only burn with a quick hot flame.
In order to demonstrate the burning properties of smokeless powder, Hatcher conducted a series of experiments in which he burned cans of smokeless powder.24 The amount of powder in each can varied from 1 lb to 8 oz. Each can was placed on a quantity of kindling wood, which was then ignited. After a period of from 40 sec to 1 1/2 min, the cans burst with a mild noise, followed by a yellow-white flame 3 to 4 ft in diameter. The underlying kindling wood was practically undisturbed. There were no violent explosions.
Black powder is a different matter. It burns faster than smokeless powder and may actually produce an explosion. Black powder is not loaded in modern ammunition. Hatcher burnt a 1-lb can of black powder. After a minute of heating, the can exploded with a heavy dull thud, producing a dense cloud of smoke but no flames. The can was hurled approximately 35 ft. It had been opened up and flattened by the explosion.
Experiments have been conducted to determine at what temperature a small-arms cartridge will detonate.25 Cartridges were placed in an oven and the furnace was heated until the round exploded. It was found that .22 Long Rifle cartridges exploded at an average of 275°F, .38 Special rounds at 290°F, .30-06 at 317°F, and 12-gauge shotgun shells at 387°F. Whereas the cartridges detonated in every case, the primers did not. In some of the detonated rounds, the primers were removed, loaded into other cartridges cases, and fired.
Occasionally one hears that an individual has been "wounded" when a cartridge was accidentally dropped into a fire and detonated. Investigation of such incidents usually reveals that the victim was really injured when they or another individual was playing with a gun. When small-arms ammunition is placed in a fire, the cartridge case may burst into a number of fragments and the bullet may then be propelled forward out of the case. In centerfire cartridges, the primer may blowout. None of these missiles, however, is dangerous to life under ordinary circumstances. The bullet in fact is probably the most harmless of all these missiles because with its relatively great mass it will have very little velocity. Fragments of brass and the primer are the only components of an exploding round that have sufficient velocity to cause injury. These fragments can penetrate the skin or eye if the individual is very close to the exploding cartridge. With the exception of eye injury, however, no serious injury should occur, and certainly no mortal wound. As the distance between the exploding round and the individual increases, the primer and brass particles become harmless because of their relatively small mass and irregular shape, which produce rapid loss in velocity.
The aforementioned observations were verified in a series of experiments in which flame from a propane torch was applied to a total of 202 cartridges: 10 shotgun shells (.410 and 12 gauge); 30 .22 Long Rifle cartridges; 68 handgun cartridges from .38 Special to .44 Magnum and 94 rifle cartridges from .22 Hornet to .338 Magnum.26 Heat applied to the base of the shotgun shells caused the primer to detonate, igniting the powder and rupturing the plastic hull. Any pellets expelled had a velocity too slow to record on a chronograph. When the primers were expelled, they had an average velocity of 860 ft/s for the .410 shells and 60 ft/s for the 12 gauge. Heat applied to the plastic hull would burn through, igniting the powder but not detonating the primers. The shot was not expelled.
In regard to the rifle and handgun cartridges, when heat was applied to the base of the cartridge case, while the primers always detonated, the powder burnt only half the time. In the instances when the powder ignited, the cases did not rupture but rather the gases were vented out the primer hole. Heat applied to the forward part of the case would cause the powder to burn with the cases usually rupturing. With few exceptions, the primers did not detonate. The velocity of the expelled bullets ranged from 58 to 123 ft/s with the exception of the .270 rifle cartridge where it was 230 ft/s. Primer velocity ranged from 180 to 830 ft/s.
Although unconfined cartridges are relatively innocuous in fires, ammunition in a weapon is dangerous if it is present in the chamber. Here we have the same conditions as if the cartridge had been fired in the weapon in a conventional manner. The heat of the fire may be sufficient to "cook off" the cartridge in the chamber. If the weapon is a long arm or an auto-loading pistol, only one round will be fired. If the weapon is a revolver, not only can the cartridge in line with the barrel discharge, other cartridges in the other chambers of the cylinder can discharge. In this situation, one bullet would have rifling marks whereas the other bullets would be free of such markings. The bullets not in alignment with the barrel would show shearing of one surface secondary to their striking the frame of the weapon as they exited the cylinder.
If one is in a situation in which a fired weapon is recovered from a burned-out residence or vehicle, it is usually very easy to determine whether the cartridge in the weapon was discharged by heat rather than by firing in the conventional manner. Examination of the primer will reveal it to be free of the normal firing-pin impression. In weapons in which the firing pin rests on the primer, a faint mark may be present on the primer as a result of slight rearward movement of the cartridge case at the time of discharge from the heat.
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Deer hunting is an interesting thing that reminds you of those golden old ages of 19th centuries, where a handsome hunk well equipped with all hunting material rides on horse searching for his target animal either for the purpose of displaying his masculine powers or for enticing and wooing his lady love.