even replacing the barrel nut wiht an extension, would be hard to do anything wrong.
Fired cases don't look wildly weird?
I"d take a brush and scrub the bolt locking luck recesses really good. I'd almost think that doing the change, somehow some crud got in there, and it could even be as small as a kernel or three of extruded powder if you ever had a round come apart in the chamber and had to push a bullet back out and had a powder spill in there or such, while fighting this issue.
Beyond that, if the barrel never moved, and you just swapped nuts and then the barrel was checked to still be seated in the reciever and would not budge, once the replacement nut was in place..
The other thought, when replacing nut, you still have to line up the gas tube... is the gas tube perfectly in line? If not it'll fight the part of the BCG that has to engage it... it will bend over, with pressure, and that might also be whats happening.
Trying to think back too, over many years and probably over a million rounds in ARs, I THINK I had a charging handle crack at the end... and bend up a hair and create some issues...I think...
