Pull the firing pin from the bolt, and look at the front edges of the stop collar on it. Could be that the hammer is catching the FP collar, and what is locking the B/C up the forward stroke.


If that is not the problem, then pull the Buffer and spring out of the receiver extension, and check the end of spring coil winds that may be scrapping down the inside of the tube, and causing the problem.  Before you put the buffer and spring back in, make sure to CLP lube the parts.

From here, pull the bolt out of the carrier, and with the carrier alone, insert it into the upper receiver all the way forward to confirm that the gas tube is correctly aligned with the carrier key.  If need and you need to correct the index of the two, tweak the gas tube over the top middle of the barrel to correct the alignment.


As for confirming that the rifle is full stroking from the start and not the problem, single round a mag, the mag inserted/round charged leaving the empty mag in the rifle, the fire for effect to confirm that the bolt locks back on the bolt catch.   If it does not lock back, pull the rifle down to clean it (with something else that Hoppes cleaning solvent since it leaves behind a residue that causing fouling problems just way too fast), including using a chamber brush by hand with CLP to clean the chamber, then lube the B/C inside and out on the wet side, insert and empty cycle the rifle a few times, which will transfer the CLP from the B/C to the upper bearing areas (CLP is the cleaning and lubing agent of choice for the platform, while the bore will need something a bit stronger to clean the copper out, and will find that something like Sweets 7.62 cleans copper out of the bore without a lot of scrubbing, and does not leave any residue behind).  After such, then try the single round stroke test alone to see if this a cleaning and lubing problem alone.

P.S. Welcome to the site!!!