I do agree with the posters on the shims under the base and zeroing using a simple eye ball bore sight.
The shims should be used to get the elevation near center at 100 yds, and probably a bit higher than center. On a Soviet scope it would be about 15% above center to enable up to an optimistic 1300 meters left in elevation adjustment.
Also, I do know that the A4 should be set windage wise to center using the windage screws on the base and typically then the left screw was staked after windage was set.
