Tech Note

September 8, 1999

TECHNICAL NOTE 34, ADJUSTING THE EJECTION PATTERN OF THE AR-10 RIFLE

Purpose:

To advise owners and gunsmiths how to adjust the ejection pattern of the AR-10B series rifle.

Background:

ArmaLite occasionally receives complaints that expended cartridges ejected from the AR-10 strike and damage the rifle’s upper receiver. The most common complaints are that the case spins and strikes either the case deflector or the front of the ejection port opening.

These ejection patterns are common to all AR-15/M16 pattern rifles. They are more noticeable on the AR-10 because the heavier cartridge case mars the finish of the receiver easier.

The ejection pattern of a rifle is created by a complex interplay of the opening velocity of the carrier group, and the extractor, ejector and their springs. In general, the faster the carrier group opens, or the stronger the extractor and ejector springs, the farther toward 12:00 (looking down on the rifle) the case is ejected. The weaker the springs are, or the slower the carrier group opens, the farther toward 6:00 the case is ejected.

ArmaLite seeks an ejection pattern between 1:00 and 3:00, and inspects for this characteristic during inspection. Obviously, the carrier’s opening velocity is subject to differences in ammunition. Springs can take a set over time, and the ejection pattern eventually shifts toward 5:00. This is normal, and readily adjusted by extractor spring replacement and ejector spring timing.

The extractor spring and plunger can be changed during routine cleaning. The ejector spring can be replaced if ejection is too far to the rear, or tuned by shortening it a coil at a time if ejection is too far to the front. Tuned ejector springs will be between a minimum of .950 and a maximum of 1.015 inch long.

As usual, selection of good ammunition minimizes complaints.

Maw

Copyright © 1999 ArmaLite, Inc.