The problem with mounting scopes on Contenders is Isaac Newton--an object at rest tends to stay at rest. You fire a round and the pistol recoils backwards, and the scope and all of its acouterments want to stay at rest. The effect is like the scope, et al, recoiling forward. As Contender barrels are tapered there's a seesaw fulcrum just forward of the front mount screws. The front of the scope, et al, wants to move down and the rear of the scope, et al, wants to move up. There's four steps to the solution:
1. Place the ring's recoil lugs against the front of the mount slots and not against the back of the slots.
2. Install a 10-32 x 1/4" or 5/16" set screw through the forward, thick part of the mount. Snug it against the barrel, just snug. Loctite it. Mark sure the rear of the set screw doesn't interfer with the front edge of the front ring lug.
3. Check all four mount screws individually, i.e., one at a time, to make sure they bottom out on the mount and not in the hole. That means install a screw, make sure the mount is tight/wiggle free, then place the screw somewhere so you can put it back in its own hole. Do that to all four screws. I will almost bet you that at least one of your screws will bottom out in its hole. Simply file down the screw's tip until the mount is wiggle free.
On my 357 minimax (long 357 mag) 10" octagon barrel, I replaced the slotted Weaver 6-48 x 3/16" screws with T-10 Torx Weaver 6-48 x 1/4" screws. It took lots of filing but the screws are there to stay.
4. So far out of three Weaver 92A mounts I have installed, on two 10" bulls and a 10" octagon, only one fit the contour of its intended barrel. The other two sat atop their barrels with a gap between. I wrapped coarse emery cloth around the barrels and moved the mounts back and forth until they mated with the barrels. Yes, it scratched the barrels.
