The problem using Weaver bases is that the slots are not wide enough to fully seat the cross bolts of (modern) rings that are sized to fit the slots on Picatinny bases. The Weaver bases must be milled out wider and sometimes deeper, or the diameter of the cross bolts reduced (ground down) to fit. A better approach might be to use an available 0MOA base, but place a shim (~.025") under the rear screws to cant the base. The amount of MOA change can be adjusted using different thicknesses of shim stock. Small washers can be used in lieu of shim stock.