yes
New Englanders have a 1:48 twist designed for sabot or round ball.
Typically a round ball .440 inches is used, together with a greased cloth patch about .015 inches in thickness. This results in a "squeeze" fit of the ball to the barrel. If you have a modern muzzle loader, we would urge you to contact the maker, and get the owner's manual for YOUR rifle- most are free, and available on line as a download. If you have an ORIGINAL muzzle loader, please do not attempt to shoot anything in it until a competent gunsmith has inspected it. And NEVER use anything but black powder (or a legitimate black powder substitute, such as Pyrodex) in a muzzleloader.
the first projectile was a muzzle loader ball discovered in 1812 and it was a 68 caliber ball
In MOST cases, muzzle loading firearms can shoot a round ball, OR a cylindrical bullet. Perhaps the best known was the "Minie ball". Named for its creator, this muzzle loaded bullet had a hollow base. On firing, the hollow base was opened by the force of the gunpowder, making the bullet sightly larger, and grip the rifling in th barrel on the way out. Google images of the Minie ball to see what one looks like.
Even when loaded WAY down, it can be unduly destructive. With a light powder charge and a round ball, it COULD be used for squirrel/ rabbit.
DO NOT ATTEMPT TO DO THIS.You may injure or kill someone.
Assuming you are talking about shooting a patched round ball, then .490 would be the most normal ball size for a 50 caliber. Of course other types of projectile might be used, such as maxi-balls or bullets with sabots, depending upon the type of gun and the purpose of shooting.
100-400 USD
Apparently Spang and Wallace did not make guns past 1845 and also made pistols. Your gun is probably a buck and ball gun and cartridges for that type weapon can be found at http://www.iusb.edu/~journal/2000/stanage.html A buck and ball gun used a cartridge containing buckshot and a ball. Either buckshot or a ball, not both at once. And certainly not in a cartridge -- it's a muzzle loader.
I assume you are looking for round balls for a 54 calibre muzzle-loader. Hornady make 530 and 535 pure lead swaged round balls. They should be available (at least on special order) from any seller who deals in Hornady products. You can also order online, although lead is heavy to ship - search for "Hornady round ball".
A 'muzzle loader' is any firearm (or cannon) which does not have a breech mechanism and which is 'charged' (loaded with powder and shot) from the muzzle end of the barrel.
a ball of metal used as a projectile in black powder, muzzle loaders