Actually, when fitting the rear, it is the "slider" that should be fitted to the hook(groove)which should be cut so that it stands "proud"of the bottom of the base.By filing the bottom of the"slider",it forces the base down.Filing the "groove",may leave movement in the assy.BTW, it can't be fitted hard against the rear of the base,since the feet swing in an arc when the scope is removed.The front base comes with the plate(when new)and they are forced together under great force by hydraulics, and they have the same radius on the plate and the hooks(they know what it is).If a hand made base is fitted to an old plate, the plate should be removed from the rifle,so it can be forced onto the hooks.If this is not done,handmade rings can give good service as long at they are used as fixed mounts and not removed often.
Mike
