This is a common problem when rifle calibers are chambered for long range pistols. I would go with the Leupold one piece mount.Have a gunsmith enlarge the existing holes to 8 X 40 and put in an additional screw. Bead blast both surfaces and glue on the receiverwith JB Weld - use Loctite 262 on the screws. The rosin sold in Brownell's will keep the scope from slipping a lot better thanthat tape they give you with the rings. Apply it with a Q-tip. The scope wants to go forward due to inertia - gun comes back violently and the scope wants stay at rest . . . Good luck. Roskoe