most if not all are bore concentric to my understanding. not 100% about the shoulders though. I guess that would depend on the manufacture. the biggest problem with most of them I thought was increased pressuredo milled AK's have concentric threads and proper shoulders on the threads?
[DOUBLEPOST=1462287052][/DOUBLEPOST]"Proper" shoulders would also be can specific too... like I know Sigs cans are different than the majority for instance.