If you need to zero a scope, build yourself one of these:
Tall Nylon screws on a flat board also work, but are more prone to flex if they are long enough to allow some scope's adjustment knobs to go around without touching the board.
All the old suggestions in this thread to shim rings (except when lapping) have the potential to ring the scope tube by squeezing it against the edges of the rings at a slight angle, which can indent it. The Burris Signature rings with the ball-and-socket principle liners that adjust to the right angle without favoring one edge of the ring or another will solve that, but that ads more expense, of course, unless you have them already.
I think if we assume a scope with at least 30 moa of elevation adjustment from center, the gun in the old original post that was still 4" low with the scope adjusted all the way up was looking about 45 moa low. If it were 1.5" above and truly parallel to the bore line, the needed adjustment for a .22 RF at 25 and 50 yards (where the zeroes cross over) would be 8.4 moa above the scope zero, as found above. The large error reported indicated a more severe problem than is normally encountered; either a bent barrel or, as suggested, reversed rings for a receiver that has about 0.040" different mount point heights for the scope rings and requires a ring set especially for that gun.