At first, I wasn't sure what you wanted info about---reenacting or buying a rifle.
I won't add to the above advice about selecting a bullet size. But I can give you some tips about molding your own.
I taught myself how to mold lead balls. I tried using the replica brass bullet molds that really had no handle at all. After many trails and errors, I have the procedure down pretty good, even though I don't have to do this but once a year or more.
You can go the old route and use a Pot and Dipper.
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But I recommend an electric furnace which drop hot lead out the bottom when you lift the lever. You will still need the Pot to transfer melted lead or to store it for next time.
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The only other thing you need is some candle Wax. Drop a pinch into the melted led and it will start to smoke and burn off the dross. Use an old spoon and skim off the black crude and you will think you have melted Silver.
TIP: Just so you don't have to learn this the hard way.
When dropping the candle wax into the melted lead, make sure you don't have wet hands. If one drop of water falls and hits that melted lead, it will Pop! out and leave a permanent tear-drop scar.
PS: I'm retired and also a VietNam- era Vet.