PMC has a rep as a little puny, and may cause short cycling in a new/tight
gun. Try some Federal FMJ before you do anything else. If the Federal
works, the PMC will probably be fine after a few hundred rounds.
Grab a box of Federal, load ONE round in mag, cycle into chamber, fire.
Bolt lock back? Done.
Short cycling. Most of the time it's gas system
Loose carrier key on the BCG.
Mis-aligned gas block---partially blocking the barrel hole
Mis-aligned gas tube where it hits the carrier key
Piston rings on the bolt head with the gaps lined up
Gunk in the gas tube. Flush it, blow it out, get some of those
l-o-n-g pipe cleaner thingies to run through it.