this report may provide for considerable savings in reducing the number of cartridge firings, while significantly lowering the rejection rate of primer, propellant and cartridge lots. The most probable causes for ignition and combustion-related hangfires were the lack of calcium silicide in the primer mix, a low output performance of primers, and finally, poor ignition sensitivity of gun propellant. Cold temperatures further reduce propellant ignition sensitivity, as well as reducing burn rate and chamber pressures. INTRODUCTION The U.S. Army's quality assurance functional test methods for the manufacture of electrically initiated 20mm munitions have not prevented hangfires. Hangfires, delayed cartridge initiations, have occurred infrequently in rapid-fire weapons at a rate averaging one in several hundred thousand firings. Misfires can be accommodated (the round is simply ejected), but hangfires have serious consequences to aircraft and other systems where such weapons are installed. Problems range from jamming the gun, effectively disarming the weapon system, to structural damage and hazards to personnel. A helicopter gunship was forced to crash land following such an incident. The electrically fired 20mm cartridge (figure 1) is used in weapons, such as the electric or hydraulic-driven M61, six-barrel Gatling gun. At the maximum firing rate of 7,200 shots/minute, the breech is closed less than 8.4 milliseconds for each cartridge firing. A delayed ignition allows the round to ignite when the breech is not seated into the barrel, during withdrawal of the round, or in the worst case, after the round is completely withdrawn from the gun's barrel. The brass cartridge case is unable to contain the combustion gases and bursts, producing damaging pressure waves and high-veloc..
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