what daryl says, chamber cast + slug the barrel
RMC https://www.rockymountaincartridge.com/i...ts%20Prices.pdf
will make you brass

and cycle fly mad wads

https://circlefly.com/products

the old eley catalogs giving a 8 ga load of 164 grains black powder and 982,52 grains shot but this depends on your shell.

reloading shotgun ammo with black powder is easy as possible. your shell or metall case having an internal space. withdraw the space for your wads and filled in equal shares with black powder and shot. thats all!