Last night I was tinkering with the rear sight on the Sharps. The sight consists of a V notch at the bottom of at 2" slide which can flip up and holds another V notch sight that can slide up and down for longer ranges. This is all held onto the barrel via a single screw in the front. The base (rear) of the sight sets in a "cradle" that is dovetailed into the barrel. I loosened the screw and cut a piece of lead shim about 1/16" thick and 3/8" x 1/2" and slid it under the sight and between the ears of the cradle.
Taking it out today I made a really good guess on the shim thickness. At 50 yards the rifle put 3 shots into a clover leaf - all touching and 3" high. That should put me pretty much dead on at 100 yards with the 500 gr bullet I'm using.
I'm still waiting for a response from Pedersoli to see what kind of rear sight options have.