So tonight, my wife and I go out to zero her AAC .300 BLK AR pistol, using Barnes factory Vortx ammo. After shot six, the bolt is locked up, out if battery. I had to take a 2x4 off a target stand to beat it open. From that point on, bolt carrier and bolt won't seat forward. Back at the cabin 100 miles from town, I disassemble and compare with a Colt 6920 upper. Both bolt carrier assemblies work fine in Colt upper. Neither works in .300 upper. YVK thinks something got loose or out of spec with the barrel extension -- this make sense? Any trouble shooting ideas, other than to send it back to AAC?