Sorry Feral have to disagree have both and would say they are quite different in many ways. AR15s will actually shoot both quite well but 7.62 is not good with sub rounds in my experience. The rifling twist is too slow and most piston semi autos such as the AK and SKS will not cycle with subs anyway. But yes 300 is stupid expensive if you don't reload but then so are many less common rounds.
Bookmarks