I wouldn't shim with metal unless you are shimming the base and not the ring. Either way I'd start off by re-zeroing the scopes horizontal reticule back to mid range before you shim (IOW, with the elevation turret back in the middle of its adjustment range). The clicks are more accurate there than at the extremes. For your situation, I'd shim the ring and leave shimming the base to if/when you start shooting that Encore at 1000 yards.
There is both tape and paper/card stock in several thicknesses with tacky surfaces available for shimming scopes, but many other things found in the average home can be used too. Any cloth tape will work, like that white cloth medical tape, and the cloth electrical black tape (not the vinyl). Even an appropriate thickness of paper will work, and can be held in place by a ultra thin coat of rubber glue (that can easily be removed from all surfaces later). Some folks even use Loctite type products on the shims, but I never found them to be necessary even on my long range handcannons. Shim(s) can be cut a bit smaller than the ring so as not to show when the scope is mounted. If you have lapped the top and bottom rings to have as near 100% contact with the scopes tube without a shim as possible, adding a shim should not cause the scope to move. I don't have it handy (out in storage someplace), but there is a formula to figure out how thick your shim needs to be. But simple trial and error will also get you there. Good luck.
L.
