AR bolt failure

[barretcreek]

Haven't had one; I am wondering what causes result in shearing a lug, a cam pin or a properly staked key. Not failures from slam fires but those from maintenance which turned out not to be good. Want to learn from other's experience.

[Bill K]

When you see photo's of bolt carriers, lugs and such ruined, broke, etc. it usually is from the party either loading over max or mixing up and getting the wrong cartridge in the AR and when it went off, more than likely with the bolt not full into battery, something breaks or blows.

[TinMan]

Not to mention that most manufacturers of those critical steel parts state that they are MPI or FPI inspected.

[Oso Polaris]

Originally Posted by TinMan

Not to mention that most manufacturers of those critical steel parts state that they are MPI or FPI inspected.

I had inexperienced shooter pick up a 300BO off the ground at range and load it into 5.56 magazine. He killed a Daniel Defense that day. The 125gr TNT, which are relatively soft with a thin jacket, cleared the 5.56 barrel. There wasn't a noticeable bulge or swell in barrel... trashed for safety. The bolt slammed back with enough force to split open the BCG like a wedge creating cracks on all sides with the bottom of it being forced downward to point of almost shearing it completely off of BCG. Extractor got bent and brass flowed back into bolt face plugging all opening (firing pin and ejector). The upper receiver cracked along front edge of ejector port to the edge of the barrel nut.

If its just lugs then usually an over-pressure issue.

I've seen a few AR failures at my LGS and most have similar look. The guns are designed to split/break and fail in specific areas to limit damage to shooter.