Suggest that before you shim that you centralise elevation adjustment ( wind all the way down and half way back).


Then set up a tall 50 yard target with an aiming mark at the top, and fire 1 or 3 rounds to measure total drop at 50 yards(1,800 inches).

Divide drop in inches by 1,800 and multiply by distance in inches between centres of your scope rings will give you a ball park figure for thickness of shim to insert between bottom of scope tube and the top of the lower rear scope ring.