I picked up a Remington Rolling Block chambered in .43 Egyptian (AKA 11.43x50Rmm Egyptian) in rough condition to play with. If brass for this cartridge is available I was not able to find it, so I tried adapting it to 45-70 government brass, hand-loaded with paper patched .442 projectiles but that did not work.
Next I reamed out the chamber with a 37/64 drill (.5781) and threaded it to 5/8-18 (this is thread used in the breech plugs of many commercial muzzle loaders, Knight, CVA and Thompson-Center being examples). I made a breech plug for the 209 shotgun primer, but the Rolling Block action does not seal well and I experienced blow back. More successful was a breech plug using the .32 H&R Magnum cartridge, and that is where my experimentation stands now. I'll probably make breech plugs using .357 Magnum (which can also use .38 Special and .357 Maximum brass) and .41 Magnum brass. I like the 5/8-18 thread because commercial bolts are available from which breech plugs can be made without having to thread the bolt.
Next I reamed out the chamber with a 37/64 drill (.5781) and threaded it to 5/8-18 (this is thread used in the breech plugs of many commercial muzzle loaders, Knight, CVA and Thompson-Center being examples). I made a breech plug for the 209 shotgun primer, but the Rolling Block action does not seal well and I experienced blow back. More successful was a breech plug using the .32 H&R Magnum cartridge, and that is where my experimentation stands now. I'll probably make breech plugs using .357 Magnum (which can also use .38 Special and .357 Maximum brass) and .41 Magnum brass. I like the 5/8-18 thread because commercial bolts are available from which breech plugs can be made without having to thread the bolt.