Yes, .741" would be ideal, but you'll have to get some brass cases from Grafs.com. Also, lube the balls with Lee Liquid Alox. 12ga slugs would be better, used with a shot cup in the plastic hulls, then you wouldn't have to worry about leading. Lyman's slug casts .704" and LEE's cast .685". If your gun was designed for black powder, then maybe you could just buy some slug loads up there and reload them.