Tech Note

May 25, 2000

Technical Note 35: Evaluating AR-10 Bolt Assemblies for Effective Extraction

A recent engineering study of the AR-10 bolt assembly concluded that marginal extraction or ejection can be caused by small errors in the location of the extractor claw. The problem is especially vexing if combined with a rough or dusty chamber (see Technical Bulletin 1, Failures to Extract from Chrome-Lined Barrels). This Technical Note provides information useful in diagnosing components in malfunctioning rifles. It must not be used to reject parts in rifles that function properly; "if it ain’t broke, don’t fix it". A caliper is required to conduct the complete evaluation.

First, test to assure that the extractor will hold a cartridge. Hook an empty cartridge under the extractor claw and use it to push the ejector all the way into the bolt face. If the extractor claw won’t catch and hold the cartridge, the claw of the extractor is too close to the breech face or the extractor groove is too narrow.

Next, test to assure that the extractor will release a cartridge cleanly. Repeat the test above, but then release pressure on the cartridge and allow the ejector spring to slowly push the cartridge in the direction of the extractor as if it were being ejected. It should pivot out from under the extractor smoothly. An interference problem is detected by a "catch" before the cartridge breaks free. In an extreme case the cartridge may actually be held in a "half-ejected" position on the bolt face. If the cartridge breaks free easily, no further inspection is normally needed.

Third, inspect the extractor/bolt relationship. Remove the carrier group and check to see that the extractor tip is flush with the end of the bolt. If it protrudes more than .0025 inch or is set back more than .0135 inch, then measure the location of the extractor pin hole in the to determine if the bolt or extractor is out of tolerance.

To check the location of the extractor pin hole in the bolt, first remove the extractor. Next, insert the extractor pin into its hole in the bolt. Measure the distance from the breech face of the bolt (the surface with the firing pin hole in the center) and the rear edge of the extractor pin. Subtract .062 inch. The result must be between .7435 and .7485 inch. If it is longer or shorter, the bolt assembly should be sent to ArmaLite for inspection or replacement. If it is between these dimensions, then the extractor is most likely the culprit.

Fourth, add the ArmaLite extractor ring to the extractor spring. This rubber ring reinforces the extractor spring and improves extractor function.

Copyright © 1999 ArmaLite, Inc.