You didn't say whether you would use black powder or "nitro for black". I don't have experience with 24 bore rifle, but do with 577 Snider. Since I don't like to use black powder, my limited experience is with smokeless powder. Smokeless powder in charges that I was comfortable with would not expand the skirts of Mini balls. This was an out and out failure. To get the rifle to shoot, I had to expand the skirts before hand so they would engage the rifling and create enough resistance for the powder to burn. To do this I made a simple ring with the inside diameter I needed( groove diameter) and with a tapered plug, expanded the skirt inside the ring, until it fit the inside diameter. This was successful , but I kept the velocity pretty low. Good luck, it looks like a fun project.