Went to the range today and confirmed what had happened before. When I change the barrel from my 45-70 to my 308 it hits within 1" of the previous zero. Of course it could be low, high, right or left but consistantly 1". When I change back to the 45-70...all bets are off are off as to where I hit. It's on paper but that's about it. Usually 4-6" in any direction. When I switch back again to the 308, I'll be about 1" off.
Nothing more than an interesting observation.