Put the barrel in a vise. Screw a Weaver type base ,on one set of holes Set a level on the base, adjust barrel in vise until action is level. Remove Weaver base, use whatever ,type base and rings that you like. Hang a plumb line at 100 yards, align vertical hair with line, fasten her down, every thing is level and plumb. I learned this while attending the University of Nyrobi.