Tech Note

December 23, 1998

TECHNICAL NOTE 3: EFFECT OF AMMUNITION ON RIFLE FUNCTION

FACTS:

1. Reliable semiautomatic rifle function requires ammunition with a variety of specific characteristics. These include:
   
   A. Proper primer sensitivity too ensures safe, reliable ignition.
   
   B. Maximum pressures within safe limits. We have been advised that certain Chinese ammunition has a tendency to detonate rather than burn at a controlled rate. This leads to excessive chamber pressure, case failure, and possible bolt failure.
   
   C. Specific pressures at the gas port. The M-16 and similar rifles require a port pressure of approximately 13,000 psi, while maintaining safe chamber pressures. Commercial ammunition oriented to bolt action rifles ignores this requirement. An apparent effort to conserve powder and keep maximum pressures low has resulted in even some military type commercial cartridges producing uneven reliability in M-16 type rifles.
   
   D. Specific physical requirements for the cartridge case. The case is made to varying degrees of hardness along its length (the "hardness gradient") which controls case expansion, chamber obturation, and chamber wall release. Commercial cartridges appear to use less brass than the strong government cartridges, and the cartridge case thus varies in resilience. Manually operated rifles do not require such stringent requirements.
   
2. Handloaded ammunition suffers a variety of possible problems. Working the case during resizing can change the case gradient and produce extraction problems. Port pressures may be either too low or too high because of a burn rate which is not suitable to self loading firearms, or because reloading manuals may specify a charge which produces low port pressures. Fatigued cases may fail. Protruding or damaged primers may be prone to slamfire or fail to fire.

RECOMMENDATION: Use only domestic factory loaded ammunition of known quality. Using handloaded ammunition voids the ArmaLite warranty.

MAW