Previously reliable AR suddenly not cycling.

[Iraqgunz]

Upon further inspection, Iraqgunz was indeed right on the money about the screw being sheared.

[Iraqgunz]

Upon further inspection, Iraqgunz was indeed right on the money about the screw being sheared.

[flenna]

Aaannndddd that's why I joined this forum.

[EVR]

Great thread.

Enjoyed reading it and as the OP says, very helpful members here.

[sundance435]

Upon further inspection, Iraqgunz was indeed right on the money about the screw being sheared.

He's a credit to the board and one of the reasons I come here first for info - also puts out a damn fine carbine. On another note, you guys have convinced me to add a full BCG to my range bag, not just a bolt.

[SkiDevil]

The screw possibly sheared and that's why it is moving, or it just wasn't staked right. My bet is on the sheared screw.

Gunz, for us un-educated folks, what would cause the screw to be sheared-off?

[MSW]

Stress corrosion cracking? Heat, gases. Not sure in nitrogen embrittlement could be a factor—i’m Throwing guesses & hoping I’gunz might be impressed by a neophyte like me

[delta6]

I had a rifle do this. The gas key was loose.

That would be the first place to look.
If it appears to you that the gas key is fine, you can check by putting a different carrier in that rifle and see if you get the same results. If the results are the same you can at least eliminate that from the mix.

[Circle_10]

Upon finding that the screw was sheared in half, as Iraqgunz had indicated, I just chalked it up to "shit happens". BCM took care of it and sent me an entirely new BCG. It's in the gun now but various forms of uncooperative winter weather has kept me from getting back to the range thus far.

[MSW]

There’s normal wear & tear, true, but the nerd in me always wants to know “why?” Why the one & not the other? Was on3 of the screws torques too tight or too loose? Was the screw alloy off? Was heat treatment off?

I admit we never know all the variables & “shit happens” winds up as the diagnosis. I’d have probably replaced both screws, torqued & staked....but my OCD meds may be off....