Re: 100 yard zero changing
So at @ 100 how tight is the grouping? When it is off by .25 moa, is it vertical or horizontal.
If the scope is good, bases etc are tight, and the lug screws torqued properly then my guess is scope to shooter eye alignment is the issue. Your cheek is not lining up exactly the same place and your eye aligment is off. This is not uncommon.