Technical Bulletin

August 10, 1999

Technical Bulletin 1: Failures to Extract from Chrome-Lined Barrels

Beginning in June 1999, ArmaLite received a number of complaints of extraction failures in AR-10A2 and AR-10A4 rifles.  The problem has been traced to normal plating roughness in the surface of the chrome-lined chambers that was not polished out during assembly.

Hard-chrome plating is not smooth and shiny, like the decorative chrome found on automobile bumpers.  It is gray, and has something of a matte finish.  Because the first motion of the empty cartridge case is straight to the rear, with no rearward camming action to break it loose, it is possible for even the fine surface roughness of new hard chrome to resist this rearward movement.

The same problem occurs in all similar rifles if an unchromed, non-stainless barrel suffers slight oxidation (rust) in the chamber or if cartridges are contaminated with dust or surface corrosion.  It is more prevalent with soft case cartridges.

The owner can correct the problem by carefully burnishing the rear ¾ of the barrel’s chamber with fine, oiled Emory paper on a closely fitting dowel rod.  In no case should the shoulder of the chamber be touched. Note that any user attempt to correct the problem is at the user’s risk.

ArmaLite will correct this problem for rifles that are under warranty. Contact ArmaLite for factory correction if that is desired.  Only the upper half of the rifle need be returned for correction and test firing.

This problem doesn’t occur with all ammunition.   It was therefore not detected during factory acceptance firing.  ArmaLite has adjusted its procedures to assure that all chambers are now polished before rifle assembly.

MAW

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