Gunpowder

Gunpowder or black powder is a substance which burns very rapidly and is used as a propellant in firearms, specifically either black powder or smokeless powder. As it burns, a subsonic deflagration wave is produced rather than the supersonic detonation wave which high explosives would produce. This reduces peak pressures in a gun, but makes it less suitable for shattering rock or fortifications.

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Black powder was the first chemical propellant and the first explosive recorded by history. Black powder is a mix of sulphur, charcoal, and potassium or sodium nitrate. Unlike smokeless propellants, it acts more like an explosive since its burn rate is not affected by pressure, but it is a very poor explosive because it has a very slow decomposition rate and therefore a very low brisance. This same property that makes it a poor explosive makes it useful as a propellant--the lack of brisance keeps the black powder from shattering the barrel, and directs the energy to propelling the bullet. The main disadvantages of black powder are a relatively low energy density (compared to modern smokeless powders) and the extremely large quantities of soot left behind. During the combustion process, less than half of black powder is converted to gas. The rest ends up as a thick layer of soot inside the barrel and a dense cloud of white smoke. In addition to being a nuisance, the residue in the barrel is hydrophilic and an anhydrous caustic substance. When moisture from the air is absorbed, the potassium or oxide turn into hydroxides, which will eat away the barrel. Black powder arms must be well cleaned inside and out after firing to remove the residue. The size of the granules of powder and the confinement determine the burn rate of black powder. Finer grains result in a closer mix of the ingredients, which results in a faster burn. Tight confinement in the barrel causes a column of black powder to burn from end to end, which is the desired method. Not seating the bullet firmly against the powder column can result in the loose powder burning all at once, which can create a dangerous overpressure condition. It is difficult to overload a black powder arm, as any excess powder will simply be blown unburned from the end of the barrel. In fact, that is a traditional method for determining the optimal loading for a black powder musket or rifle--fire it over a patch of virgin snow with gradually increasing powder charges, and look for the appearance of unburned powder grains in the snow to indicate too much powder. The lack of pressure sensitivity means that the mass of the bullet makes little or no difference to the amount of powder used. A full charge of black powder seated by just a small wad of paper, with no bullet, will still burn just as quickly as if it had a full weight bullet in front of it. This makes black powder well suited for blank rounds, signal flares, and rescue line launches.

Related Topics:
Black powder - Sulphur - Potassium - Potassium - Oxide - Hydroxides

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