Tech Note

December 26, 1998

TECHNICAL NOTE 10: PREVENTION OF SLAMFIRES

FACTS:

1. A slamfire is the unintentional discharge of a cartridge during loading or locking, without normal hammer or striker fall.
   
2. Because of inertial energy remaining when the bolt closes, the firing pin of a number of rifle models such as the Ml rifle and carbine, M-14 rifle, and most ArmaLite patent rifles, strikes the cartridge primer lightly upon chambering a round. This light strike normally will not cause the primer to fire, but it is possible. Government 5.56mm (.223) cartridges are loaded with a thick cupped primer to provide assurance that such an occurrence is rare. Government and commercial 7.62mm (.308) primers are not hardened in this manner.
   
3. The AR-10B design includes a firing pin spring which reduces the inertial energy of the firing pin to a very safe level. Extensive firing has confirmed that the firing pin spring almost totally cures slamfire without reducing ignition reliability. No case of slamfire or misfire has been observed in an AR-10B equipped with the firing pin spring.

RECOMMENDATIONS:

1. When feeding single shots, feed cartridges only from the magazine, or use the charging handle to lower the carrier closer to the closed position before releasing it.
   
2. Assure that the firing pin retarding spring is installed before firing the AR-10B. It is an important safety device. Never fire the rifle without it.
   
3. Always assure that the barrel is pointed in a safe direction when loading any firearm.
   
4. Use only fresh, good quality factory loaded ammunition.

MAW

© 1998 ArmaLite, Inc.