Pull the bolt off the carrier and try just the carrier alone in the upper receiver(face of it touching the face of the barrel extension). This will tell you if the gas tube is aligning with the carrier key correctly or not the last inch of forward movemet. If its the last inch forward that is the problem, then the gas tube needs to be tweaked just above the center of the barrel under the hand guards to solve the that problem.

If the carrier is binding all the way down, then it's the key or cam that is too wide, and by looking for rub marks, will be able to tell which piece needs to polished or lapped.


Now take a good look at the center of the barrel feed ramps against the front take down lug. Is the center line of the feed lips dead center of the lug, or did the barrel slip on install, and now the barrel canted in the upper receiver barrel socket.


At this point, now lets address the bolt.

Start off by looking at the back of the gas bugle section of the bolt, is the straight section of the tail of the bolt a clean plain, or is there a step in the straight section just before the bugle section that is catching on the carrier channel for it when the bolt goes to lock up. If you find such a increased surface, then it need to be reduced back down to the rest of the bolt tail straight.

Now lets take a look at the front and back edges of the bolt locking lugs, and may be even a bit of dry fitting of the bolt to the barrel extension without the carrier. Brand new, on some combo's the bolt lugs need to mate in with the barrel extension before the bolt is going to glide very smoothly at unlock (read a bit of live fire solves that).

If you have not fully cleaned and lubed the rifle per the operation specs, now would be a great time to do such. The rifle is packed in protective lubes to prevent storage rusting, and such lube can be packed with shop debris as well. If you did not get a cleaning manual with the rifle, then we have a whole forum dedicated to such. Also, the problem now could be as simple as a blow primer that has found it way in the barrel extension void.

Lastly, if you have a L cut hammer and an un-shrouded carrier, then you do need to take a look at the firing pin stop collar against the carrier ramp. The edge of the FP stop collar needs to be flush or slightly below the ramp so the hammer will not catch the FP during forward travel.