Couple of things- neither of which is gas system.
Your rifle uses a rotating bolt. Be sure that you have cleaned the bolt, and that there is lube betwen the bolt and bolt carrier.
Second- firing pin. Be sure that FP and FP channel are clean, LIGHTLY lubed, and the FP is correctly installed.
Possible bad news- check the recess that bolt lugs turn into- use tip of pinky. Feel for roughness, burrs. If it has galled, will make it difficult for bolt to cam into place. Now, look at pinky. Crud? Those recesses get missed in cleaning.
ALSO- Important note- there WAS a safety recall on those, fixed by replacing firing pin. Original can have tip break, wedge into bolt, resulting in uncontrolled full auto fire. If you do not know if yours has been fixed, remove mag, turn weapon so you can look into the mag well, draw bolt back, look for letter stamped on the inside of the "roof".