Well, isn't this why we love building/modifying/restoring these things? I'm working through putting a MBS cast brass butt cap on a Pedersoli Kentucky pistol kit, and here's where things stand. The butt of the stock was not shall we say...perfectly symmetrical so one side is a little fatter than the other, I'll keep filing (love those files and the occasional very sharp inletting chisel) to lower the rear of the cap so that it sits mostly on the pistol butt. I'm thinking I might have to bend the sides of the cap inward just a bit. Suggestions from the Builder's Bench Brain Trust are welcome if anyone has worked through this issue. I think I can get there eventually but any hints will help...looking at photos from various books on the "Kentucky pistol" I see that butt cap placement can be rather odd from time to time so I guess I'm in good company!