Kutter,
The original 6.5x55 is larger, but my brother bought American made commercial cases for his, and they had 06 headsize(I guess to avoid new tooling).It worked fine, after expanding to chamber size.So,new American 6.5x55 ammo may almost chamber in 257 chamber.BTW Cerrosafe does shrink, at first, but after some time it expands to original dia.This drill points out the importance of marking the caliber on the barrel.It is easier to make a chambercast if you pull the barrel first( add witness mark if not one already).
Mike
