This AR is in 5.56 and when shooting .223 ammo through it, it hangs about every third shot. Would that be do to lower pressures in the .223 or does the gun have problems? I haven't fired 5.56 ammo in this gun yet (can't find any local yet).
Check the 2 screws on the gas key (the dog-legged thing on to of the Bolt carrier)
The must be very tight and staked in place to stay that way. If they are a bit loose the gun will malfunction as you describe.
I don't think pressure is the issue. What the last two said seems like a good culprit.
However. I must ask if you lube the bolt carrier and the upper received. If so don't for a free hundred rounds. Leave a it dry. And fire a few hundred through it. After a time it will become polished by the force of the action and feed more reliably.
At least that was my experience in Afghanistan. Deployed with a brand new colt m4. Once you fire a few hundred rounds bone dry and make sure every thing on the fire arm is peachy it will function without fail.
