I've always heard that you want the scope as close to the bore as possible and if I recall, some factory ammo stipulates a 1.5" scope height when giving ballistic info. If you have a big 50 or 55mm on the end of the scope, it may not have enough clearance and wind up laying on the top on the rifle, again I'm told thats no good either, and you need a riser to get it off the bore higher.
