The Peabody in 10.4X38mm (.41 Swiss) is an excellent round and may be loaded with approx. 40 grains of 3F blackpowder, or with one of the suitable smokeless powders. Brass may be had from Buffalo Arms and centerfire breechblocks could be had at Dixie Gunworks for $15 a few years ago. They are all gone now. If it's a rimfire the conversion of the breechblock is simple for a machinest, but the firing pin is the trick. They are wonderful little rifles and mine was good to 200 yards.