Tech Note

TECHNICAL NOTE 32:   Identification and Correction of Malfunctions

This technical note has been prepared by the Quality Assurance Division of ArmaLite, Inc. It is based on ArmaLite's experience and on government documents produced over the past 30 years. While it doesn't cover every possible problem, it will help correct the vast majority of problems found. This summary is logically based on the "Cycle of Operations" common to all firearms. It is applicable to almost all firearms.

The focus of this note is on rifle malfunctions, not ammunition malfunctions. The effects of faulty ammunition (damaged, dirty, poor ignition or insufficient pressures) should be fairly obvious, and are generally deleted for the sake of brevity.


Failure to feed and chamber first round
Description:
This failure occurs when the bolt is released and it fails to chamber the first round from a loaded magazine
Cause:
This malfunction is usually the result of accumulation of dirt or fouling, a defective magazine, an improperly inserted or improperly loaded magazine, or a damaged round. In the case of an improperly loaded magazine the projectile end of the top round in the magazine often becomes inadvertently tipped down. This is often known as a "stubbed" round.
Corrective Action:
The bolt should be retracted and held to the rear while the magazine is removed and the malfunction cleared. The rifle should be field stripped, cleaned, and lubricated. The magazine should be replaced with another if malfunctions recur.

Failure of cartridge to fire
Description:
Failure occurs when the firing pin either strikes the primer with insufficient energy or fails to strike the primer at all.
Cause:
Full forward travel of the firing pin is restricted. This occurs when the bolt carrier fails to fully close and the hammer strikes the carrier rather than the firing pin. The hammer striking the carrier may cause the carrier to move fully forward and, on inspection, the cause of the malfunction in not then apparent
Corrective Action:
If this malfunction becomes repetitive, the firing pin, bolt, and bolt carrier should be inspected. The firing pin tip should also be inspected for damage.
Cause:
Broken hammer spring. The hammer spring has two coils, with legs protruding from them and over the trigger spring. If one coil or leg of the hammer spring is broken, the spring energy applied to the cocked hammer is insufficient to reliably fire the cartridge. This malfunction will produce intermittent malfunctions.
Corrective Action:
Replace the hammer spring.

Failure to completely eject a fired case

Description:
A malfunction occurs when the fired case is not successfully cleared through the ejection port and becomes jammed in the mechanism as the bolt closes. Occasionally the fired case, while initially clearing the gun, may strike an outside surface and bounce back into the path of the bolt. This is referred to as "spin-back".
Cause:
Ejection failures are often related to a weak or damaged extractor spring and, much less commonly, to a weak or damaged ejector spring. Failures to eject can also be caused by an accumulation of carbon or fouling on the ejector spring, on the extractor, and from short recoil. Short recoil is usually due to an accumulation of fouling in the mechanism.(short stroke may also be caused by a fouled or obstructed gas tube). Difficult extraction from a fouled or corroded chamber can also cause ejection failures.
Corrective Action:
If repetitive malfunctions occur and are not corrected by cleaning and lubricating, it is recommended that the ejector spring, the extractor spring, and the extractor be replaced even if damage is not apparent. The ejector itself does not often require replacement.
The determining factor in deciding whether a failure-to-eject or a failure-to-extract has occurred is the nature of the clearing action required to overcome the malfunction. If the fired case can be cleared by simply retracting the charging handle, a failure-to-eject has occurred; if difficulty is encountered to the extent that repeated charging handle cycles are required or if tools are required to clear the malfunction then a failure-to-extract has occurred.

Failure of a fired case to be successfully extracted from the rifle chamber.

Description:
A failure to extract results when the fired case remains in the rifle chamber
Cause:
Short recoil cycles or fouled or corroded rifle chambers are the most common causes of failures to extract. A damaged extractor or a weak or broken extractor spring can also cause this malfunction.
Corrective action:
Where cleaning and inspection of the mechanism and the chamber reveal no deficiencies in these areas, and failures to extract persist, the extractor and extractor spring should be replaced. If the chamber is tight polish out with steel wool, or run finish reamer in to clean up the chamber (of unchromed barrels only) then polish afterwards. If surface has major damage replace the barrel.

Failure of a live round to be successfully stripped from the magazine and fully chambered

Description:
This malfunction occurs during a firing sequence.
Cause:
The majority of feeding failures is due to one of two causes; short recoil or a defective magazine. In short recoil, the bolt lacks sufficient energy to move fully rearward to engage the cartridge base, or, with the base engaged, lacks sufficient energy to complete the feeding operation. Magazine failures are most often caused by damaged feed lips that present the
Corrective action:
The bolt should be retracted to the rear and then the magazine is removed and the malfunction is then removed.

Failure of the bolt to remain in a rearward position, engaged by the bolt catch, after the last round has been fired

Description:
The rifle appears to be in a normal, bolt-closed position.
Cause:
The malfunction is most commonly due to short recoil; this failure is also occasionally due to a high cyclic rate of fire where the bolt catch does not have sufficient time to move into position.
Corrective action:
Cleaning, inspection, and lubrication of the mechanism, including the bolt catch assembly, should be accomplished when repetitive failures occur; in the event of continued failure, the bolt catch and spring should be replaced.

Miscellaneous malfunctions

The firing of two rounds on a single trigger pull.

Causes:
This is often due to the trigger pin backing out from engagement from one side or the other of the receiver. Loosening of the trigger pin in turn is due usually to a broken or to an incorrectly assembled hammer spring. The sear surfaces of the trigger or hammer may be worn and prevent full sear action. The disconnector hook and/or the disconnector surfaces on the hammer may be worn, allowing doubling. The disconnector spring may be weak.
Corrective action:
The hammer spring should be inspected for damage or incorrect assembly. Replace the hammer and trigger if their engagement doesn't provide positive hammer retention. The disconnector and/or hammer should be inspected for wear that would interfere with safety, and replaced if needed. The disconnector spring should be replaced.


Failure of trigger to return to forward position after trigger release.

Causes:
This is usually due to dirt or an accumulation of fouling in the mechanism, lack of lubricant, or a broken trigger spring.
Corrective action:
This requires disassembly, cleaning and lubrication, or replacement of the trigger spring. In some instances, due to improper engagement surfaces, the hammer and disconnector may require replacement.

This document will be updated periodically.

Copyright © 1999 ArmaLite, Inc.