You're off to a good start! My mold drops a .545 diameter. Too large, so I'll be looking for a sizer. A .540 and a .538. My bore is .540.
Minie rifles typically have shallow rifling. Originals had progressive depth, starting at .015 in the breech and ending at .005 at the muzzle. Gave the fouling a place to go.The .005- .006 of the 1-48 T/C barrel is fine for minies and conicals. Match the length in relation to diameter to the rifling and have a(n) ( elongated) ball!
The twist rate for rifle muskets, aka 3 bands, was typically 1-78. In theory, not sufficient to stabilize the minie. BUT! The hollow base of the minie puts its weight forward, so it drag stabilizes. Think badminton birdie. As it tries to pitch/ yaw, air resistance pushes it back in line.The 33 inch rifles, usually issued to sergeants, were 1-48. The faster twist fouled more in combat, but sergeants weren't expected to do much shooting. The 1-48 was more accurate though.