Powder Lifetime

 Questions about powder lifetime and deterioration keep appearing. Here are some answers from a chemist's point of view. Black powder is a mixture and not subject to deterioration with time, black powder made in the Civil War still works and fixed ammunition made in the 1800's will still fire, the limiting factor is the short life of older priming mixtures. Moisture is the primary enemy of black powder, wet black powder is inert. Moisture can leach the soluble nitrate out the powder rendering the powder inert or low power even if it is dried out. Single base nitrocellulose powders are water resistant and double base powders with both nitrocellulose and nitroglycerin are water proof. Just dry them out and they will work as intended. Acid is the enemy of smokeless powder. Nitric and sulfuric acid are used in the manufacture of smokeless powder and great effort is expended to remove residual acid from the powder. However both nitrocellulose and nitroglycerine undergo auto decomposition and this decomposition releases the nitrate groups as which are acid. This acid then attacks the nitrocellulose and accelerates the decomposition in an ever quickening cycle. This decomposition generates heat, which in small containers of 100 pounds or less is dissipated, but in large (tons) military storage of bulk smokeless has caused fires. The acid released will also attack metal and often the first indication of powder deterioration is rusting of the inside of metal containers. The decomposition products are a brown or black fine powder, and the sharp smell of decomposing powder is caused by the acid released. In order to extend the life of smokeless powders, manufacturers incorporate stabilizers which react with the acid before it can attack the nitrocellulose. The most common stabilizers are diphenyl amine and calcium carbonate. However there is a limit to the amount of stabilizer which can be employed. The stabilizer reduces the energy of the powder and hard deposits from the calcium carbonate have caused problems in gas operated automatic weapons. Stabilizers are usually present at less than 2% by weight. The stabilizer is used up as the powder molecules slowly auto decompose, but the acid is prevented from attacking other nitrocellulose molecules. Eventually the stabilizer is depleted and the released acid then attacks the remaining nitrocellulose which releases more acid in an increasing cascade. This is the reason smokeless powder is good for years and then will go bad very suddenly. Vihtavuori states to expect a lifetime of a minimum of 10 years at a temperature of 20 C (68 F) with their powders. The auto decomposition is temperature dependent, and a general rule for exothermic reactions is they double in reaction rate for every 10 degrees centigrade increase in temperature and slow down by half for a 10 C decrease in temperature. Therefore we expect the following powder lifetimes using what is a conservative estimate by Vihtavuori: 50 F - 20 years 68 F ”€œ 10 years 86 F ”€œ 1 year 104 F - ~ 1 month 122 F ”€œ 3 days Of course temperature is rarely constant for long periods, but the stabilizer is being depleted so temperature exposure is cumulative.  This explains why my friend, whose un-air-conditioned reloading shed would hit 115 F on a hot summer day, experienced powder going bad in 4 to 5 years. So guys and gals, keep your black powder dry and your smokeless powder and ammunition cool. Steve Hurst