I have not worked with this cartridge, but I have used slightly smaller than bore size bullets with black powder and gotten good accuracy. Since the x72 started with BP, it might be fun to try. My most recent project was in an 11.75x61R cape gun. The things I've found success with are plain base soft bullets (1 tin-20 lead), a milk carton wad on top of the powder, a pea of bullet lube (I used Lyman's old black colored lube) and compressed powder. I was able to get working groups at fifty yards with pretty coarse old sights.
Another option would be paper patched 357 diameter cast bullets. The 200 grain lyman might be a good starting point.
Bfly
