Strange AR problem

[rimlick]

So I have an issue with my bolt locking back when I still have rounds in the magazine.

The only thing I can imagine is the bolt catch pops up if the recoil is bad and sharp enough.

Is this a symptom of the rifle being over gassed? It is a 7.5" barrel.

The other theory is the bolt catch spring is weak, but I did shim it with a 1/2 mm piece of metal to simulate ever so slightly more spring pressure and it didn't seem to help. Still. Maybe I just need a new spring?

 

[Still alive]

Do you shoot gripping the front of the lower receiver? Is it possible your thumb is riding the paddle?

 

[hbean]

see if the face of your hammer is hitting the back of your bolt catch and keeping the bolt catch up.

 

[*MALICE*]

Also check to see that the spring/detent hole for the bolt catch is not peened over.
My buddy (somehow) had that happen and it kept the detent captive (not pressing against the bolt catch) sob the bolt catch would bounce around and randomly lock the bolt back.

......you don't have a bad lever attached....do you?

 

[y2k]

Interesting

 

[Lexthedestroyer]

Does the bolt catch move freely when the lower is detached from the upper? Dry firing the lower without the upper installed can "dent" the channel that the bolt catch moves in.

 

[Cameron SS]

So I have an issue with my bolt locking back when I still have rounds in the magazine.

The only thing I can imagine is the bolt catch pops up if the recoil is bad and sharp enough.

Is this a symptom of the rifle being over gassed? It is a 7.5" barrel.

The other theory is the bolt catch spring is weak, but I did shim it with a 1/2 mm piece of metal to simulate ever so slightly more spring pressure and it didn't seem to help. Still. Maybe I just need a new spring?

Overgassed alone is not your problem. Even if your rifle is gassed properly, it should be travelling far enough rearward to pass over and catch the bolt catch.

Is the problem intermittent, or does it happen every shot?

The bolt catch spring may be weak, but a weak spring on its own should still be pulling the bolt catch into the retracted position.

First, we need to identify why the bolt catch is getting pushed up into the position to engage the bolt. Normally this is done by the magazine follower, or the bolt catch. So check your mags to make sure they aren't doing anything weird. Otherwise as others have suggest, what could be pushing up on the bolt catch? Could it be you? with handgrip on the magwell, or with a bad lever?

I'd take the upper off and just play with the bolt catch. does it move freely? does it stick? does it grind? As far as springs go, the bolt catch spring is a very low tension spring, but does it retract the bolt catch well, or does it seem lazy.

The effect of recoil bouncing the bolt catch would be instantaneous. I'd like to think that its a pretty bizarre coincidence that recoil would defeat a weak spring at the exact moment the bolt is in position to be locked up by the bolt catch.