My AR has become a straight pull bolt rifle.

[bernie]

I understand pretty well how an AR works, but certainly could stand to know more. I have a .300 Blackout with 16” barrel that I built a few years ago. It has a pistol length gas tube and has run well for a while. Recently it started malfunctioning on every shot. It will kick out the brass but the bolt does not travel far enough to strip the next cartridge from the magazine. Everything looks normal except for two things. The fist is there is some carbon build up on the right side of the gas block where the roll pin holds the gas tube in. The second is there is some slight damage to the front of the gas key as it is apparently striking the rear of the gas tube. I would assume the second thing is the issue. Do you guys have any other ideas?

 

[NIGHTLORD40K]

Broken gas (piston) rings on the bolt, carbon buildup at the port, block shifted on the barrel due to loose pins.....things to check. Come to think about it, that last might explain the leakage at the roll pin and misalignment at the key.

Might want to check the barrel nut too.

 

[BBBBill]

I have a .300 Blackout with 16” barrel... Recently it started malfunctioning on every shot. It will kick out the brass but the bolt does not travel far enough to strip the next cartridge from the magazine. Everything looks normal except for two things. The fist is there is some carbon build up on the right side of the gas block where the roll pin holds the gas tube in. The second is there is some slight damage to the front of the gas key as it is apparently striking the rear of the gas tube...

As Nightlord mentioned above. I would first focus on fixing the two items you found. Niether is correct and fiddling with anything else while those problems are still there will confuse your repair efforts. Ensure that the gas block is correctly oriented and tight on the barrel, the gas tube is not leaking where attached to the gas block, and make sure that it is correctly aligned going into the receiver. All of that starts at the gas block. That's a major reason that I prefer pins instead of set screws hold my gas blocks. Preferred, but no all of mine are.... yet.