I've never run into this problem before. The go and no-go gauges fit into a 7.62 barrel just fine but a live round won't go in far enough for the bolt to rotate. I've tried several rounds and even two different brands of ammo. I'm wondering if this means the barrel is at fault and needs to be reamed. The barrel is from a Mac 90. I tried cleaning but that didn't help. I hate to pin the barrel until I get this figured out. Is there somewhere I can send the barrel to get this remedied. I'm completely at a loss.