Where does the bolt come to rest against the cartridge? Behind it, still trying to push it up the ramp, or does it override the base and come to rest against the body of the case?

Is the gas key on your bolt carrier loose?

Is your gas tube loose where it connects to the front sight base?

Is the gas tube off center or not coming back far enough in the upper receiver? Compare with pictures of other ARs on a google image search.

Have you tried a different brand or lot of ammo?

Are all three gas rings present on the bolt? Any deformation or damage?

Any obstructions in the receiver extension, aka buffer tube?


Ignore the "advice" above to get a heavier buffer until you find out the real cause for your malfunction.