rcmodel is probably exactly right about what's going on. You mentioned using the P-Mag. These are known to work very well with these guns. You might check the bottom of your bolt for rough spots or burrs that might be rubbing the feed lips or the next cartridge. If this is a new gun, it may get better on break-in. Mine shoots from full 30-round mags. I polished the bolt on it and it helped reliability. If I were using my PLR-16, or AR-15, for defensive purposes, I would consider downloading a round or two as well.