I've got a new AR and old AR. The old Bushmaster DCM runs flawlessly, several times I've abused it by going over 2000 rounds between cleanings and it just keeps shooting little groups. My new AR is an CMMG 18"SPC upper and Bushy lower and I can't figure out why it short strokes about 20% of the time. I've checked for the correct buffer and spring, gas key and block leaks, it's clean and lubed properly, and is fed full powered ammo. I took both guns apart side by side to compare and feel the parts and the only difference I could find was in the bolt carrier group. The CMMG bolt is buttery smooth locking and unlocking in the bolt carrier while the old abused Bushy has a definite detent feeling as it locks and unlocks. I'm not very knowledgeable when it comes to the AR platform, can anybody send me in the right direction?