the very first round! the extractor broke the lip off the Monarch Steel case ammo i was using. Had to use a brass rod down the barrel to knock the round out. Happened on the second round too. After that, the rounds were ejecting pretty well but, the hammer wasn't cocking. I changed out the buffer from the Spike's ST-T2 to a normal buffer but problem persisted. I had to manually work the action and take out the live round that was loaded without the gun being cocked. I found that EVERY round that was loaded without cocking the action had a nice dimple in the primer though. A firing sequence went something like this: Shoot, round ejected, live round loaded. pull trigger, nothing. gun uncocked. pull back charging handle, eject live round with dimpled primer. Let CH fly loading new live round, gun cocked. Shoot.....and so on. I switched out the CB lower to my AR/K and had the same problem with the 7.62 upper. The Stag lower i had worked fine on the AR/K. i didnt have enough rounds with me to get deep into it and i had a guy with a 45 going hog wild with rapid fire......(no comment) the few rounds i ran the Stag lower on the 556 upper did pretty much the same thing. So, to clear up the confusion i have wrought.... CB lower on 556, shoot, eject. manually work action. shoot. Stag lower on 556, same thing. CB lower on 762, same thing. Stag lower on 762, ran like a champ. So, i am thinking i may have two problems here. One on the CB lower and the other on the 556 upper. i dont know. i was concentrating so hard on getting the rifles sighted in and then the casing jammed. i switched over to the 762 after 20rds of 556 so didnt have much time to investigate further.