jscb1b, I had the exact problem. First, the S&B ammo is crap. Second, the jam issue ended up being the PMAG magazines. The mag wouldn't position the round high enough in the receiver, so sometimes it would strip the round out of the mag by the case body vs. the case head. It would then wedge between the bolt and the barrel extension. Used the Lancer L7-AWM mag so solve the issue. Good luck.