Alright,
Here is a simplified reply to your questions…. Please forgive me if it’s so simplified that’s my writing sounds a bit silly....,
So a Minie Ball is a length of lead with a tapered tip, which we today would look at and say “bullet”. Technically, the projectile from a rifle or pistol whether they are a round ball which is a sphere, a flat nosed bullet, or one with a rounded or pointy nose, are all bullets.
More than a century and a half in the past, A French Army officer, Colonel Claude-Etienne Minié designed a new projectile for military rifles and a simpler, faster reloading, so the bullet is named after him and called a Minie-Ball today. Sounds like “Miniball” but there is nothing minimized about them. Not only being heavier, and better when flying through the air than a sphere, the design worked because the base of the bullet would engage the rifling, so the bullet would be spinning and stable when it flew from the rifle muzzle, and thus accurate.
View attachment 177500
A round ball when used in our traditional rifles, is smaller than the bore size of the barrel. SO, to get the ball snug enough inside the barrel so that the ball will be spinning for stability and thus flying stable and accurate toward the target, a “patch” is wrapped around the ball. This is normally a piece of cloth with some sort of grease on it. This acts like a gasket, and also helps the ball engage the rifling.
View attachment 177501
The rifling, the grooves cut into the inside of the barrel of the rifle, impart a spin to the bullet, very very similar to an American football being thrown in a forward pass. The spin on the bullet or the spin on the football, makes it much more stable as it flies downrange. A plain barrel had the grooves cut when it was made into a rifle barrel. The cut areas are called the grooves, but the remaining areas are called the lands. The patch gets the ball snug against the lands, but since it also is touching the grooves, when the patched, round ball is fired, the ball spins in keeping with the twisting of the grooves within the barrel.
View attachment 177503
So a "normal" muzzleloader bullet , here in the Traditional Forum is a patched round ball.
Your rifle is a reproduction of a Civil War Rifled Musket... we'd call it a "rifle" today, and it's "normal" bullet is a minie-ball.
There are other bullets out there that will likely work. For example, the Lee company makes bullets and molds to make your own bullets, called the REAL bullet. "REAL" stands for "Rifling Engraved At Loading", and those bullets will also engage the rifling and spin when shot.
Thompson Center company came up with the Maxi-ball, and the Maxi-hunter, very similar to the antique style minie-ball. They work well.
Hornady makes their own bullet, known as the Great Plains Bullet.
There are a lot of options, all of the above are good choices, but here we don't use modern, jacketed bullets, nor do we use sabots. Which one should you use? Well the most accurate one, but you won't really know until you test them out. The patched round ball is often very accurate, and often has the less recoil, but it's the slowest when loading. The more modern bullets like the minie-ball or the Maxi-ball, are quicker when loading, but may kick more.
LD