I had Hamilton Bowen build my K .327 Magnum using a Model 16-4 barrel, a rechambered Model 17 cylinder and a pre-Model 15 5-screw frame. That was the simplest and most affordable route at the time. There is no simple way for you to 'reline' a Model 15 or 19 to a smaller diameter cartridge. The extractor wouldn't work. You'll want a Model 17, 18, 48, 53, 617, 618 or 648 cylinder.