Probable Cause

Action/Remedy

 

Failure to feed
ammunition.

• Lack of lubrication of operating parts.
• Defective or worn parts.
• Short recoil.

• Clean and lubricate parts.
• Replace parts.
• See ‘short recoil’ under stoppage/malfunction list.

• Lack of lubrication of operating parts.
• Dirty chamber.
• Defective ammunition.

• Clean and lubricate parts.
• Clean chamber.
• Replace ammunition.

Failure to lock bolt.

• Lack of lubrication of operating parts.
• Dirty chamber.
• Dirty locking recesses.
• Weak op rod spring.

• Clean and lubricate parts.
• Clean chamber.
• Clean recesses.
• Replace op rod spring.

Failure to fire
ammunition.

• Defective ammunition.
• Defective firing pin.
• Defective trigger housing group.

• Replace ammunition.
• Replace firing pin.
• Repair trigger housing group.

Failure to unlock bolt.

• Dirty chamber.
• Lack of lubrication of operating parts.
• Insufficient gas.

 

• Follower arm pin worn.
• Follower arm bent or out of tolerance.

• Clean chamber.
• Clean and lubricate parts.
• Tighten gas cylinder lock screw, and/or clean or replace
worn parts.
• Replace follower arm pin; verify pin hole diameter.
• Replace follower arm.

• Dirty chamber.
• Defective ammunition.
• Broken extractor.

• Clean chamber.
• Replace ammunition.
• Replace extractor.

Failure to eject
cartridge case.

• Broken ejector or spring.
• Short recoil.

• Replace ejector or spring.
• See ‘short recoil’ under stoppage/malfunction list.

• Defective trigger housing group.
• Short recoil.

• Repair trigger-housing group.
• See ‘short recoil’ under stoppage/malfunction list.

Cartridge clip inserts
with difficulty.

• Deformed cartridge clip.
• Broken clip ejector.
• Interference between bullet guide and
follower arm.

• Replace.
• Replace.
• Replace bullet guide or follower arm.

 

 

• Undersized or out of round op rod piston.
• Oversized gas cylinder.
• Undersized barrel at gas port.
• Carbon in gas cylinder.
• Carbon or foreign matter in gas port of
barrel.
• Op rod assembly binding.

 

• Leak in gas cylinder lock screw with
valve.
• Defective op rod spring.
• Bolt binding.
• Distorted or damaged receiver.

• Replace op rod assembly.
• Replace.
• Rebarrel firearm.
• Clean.
• Clean.

 

• Replace op rod assembly if damaged, or relieve wood
from gun stock assembly, where op rod binds on wood.
• Replace gas cylinder look screw with valve.

 

• Replace op rod spring.
• Remove burs from bolt.
• Repair or replace receiver.

• Extractor does not open enough to pass
over rim of cartridge.
• Op rod assembly binding.

 

• Weak or broken op rod spring.
• Rust or dirt in chamber.
• Damaged cartridge, or frozen ejector.
• Damaged/deformed bolt and/or receiver
• Insufficient headspace.

• Clean bolt assembly.

 

• Replace op rod or relieve wood from stock assembly
where op rod binds on wood.
• Replace op rod spring.
• Clean barrel chamber.
• Repair or replace ejector.
• Replace bolt or receiver.
• Replace bolt assembly by selective fit or headspace.

 

• Insufficient radii or burs on op rod catch
or op rod hooks.
• Bullet guide low at accelerator bearing
point.

• Repair or replace op rod catch or op rod assembly.

 

• Replace bullet guide.

 

 

• Worn or broken clip latch.
• Worn or broken clip latch spring.
• Excessive radii on op rod catch or op rod
assembly
• Bullet guide high at accelerator bearing
point.

• Replace clip latch.
• Replace clip latch spring.
• Replace op rod catch or op rod assembly.

 

• Replace bullet guide.

 

 

• Worn cartridge clip detents.
• Weak clip latch spring.
• Worn clip latch.
• Bent follower rod.
• Worn follower rod forks.
• Worn or deformed op rod catch.
• Worn follower arm.
• Follower rod rubs on op rod catch.

• Replace cartridge clip.
• Replace clip latch spring.
• Replace clip latch.
• Replace follower rod.
• Replace follower rod.
• Replace op rod catch.
• Replace follower arm.
• Replace follower rod, clip latch, or op rod catch.

• Bolt does not move sufficiently rearward.
• Binding clip latch.
• Arm or op rod catch bent or deformed.

• See ‘short recoil’ under stoppage/malfunction list.
• Replace clip latch.
• Replace op rod assembly.

 

 

Failure to eject spent
cartridge case.

• Low power, causing short recoil.
• Weak, missing, or frozen ejector spring.
• Ejector binds.
• Short recoil.

• Correct ‘short recoil’ stoppage/malfunctions list.
• Replace ejector spring.
• Clean bolt ejector opening or remove burs from ejector.
• Clean gas port. Replace op rod assembly or helical
spring.

• Clip ejector worn, weak, or broken.
• Op rod catch deformed or broken.

• Replace.
• Replace op rod catch.

• Plugged gas port.
• Loose gas cylinder.
• Barrel undersize at gas port area.
• Gas cylinder lock screw with valve fails
to close.

• Clean gas port.
• Replace gas cylinder.
• Replace barrel.
• Replace gas cylinder lock screw with valve.

Failure to fire.

• Light indent on primer.
• Inadequate firing pin protrusion.
• Hammer spring housing damaged.

• Replace hammer spring.
• Replace firing pin.
• Replace hammer spring housing.

• Deformed trigger, pin, or hammer.

• Replace defective trigger, pin or hammer.

• Op rod assembly releases too soon when
clip is inserted.

• Replace op rod catch and/or bullet guide.

 

 

• Worn op rod lug or kinked op rod spring.
• Receiver op rod guide rail excessively
worn.

• Replace op rod assembly or op rod spring.
• Replace receiver or rebuild receiver guide rail.

• Defective ammunition.
• Wrong ammunition.
• Incorrect barrel chamber dimensions
(headspace).

• Replace.
• Replace.
• Properly headspace or rebarrel and headspace.