this is a 3 ring minne ball, shot drom a rifled muzzle loadser , probably a 56 or 57 caliber, one of the more common shots,used after the civil war also. still a great fine has great patina, do not clean it, you will kill the value.it was used by both sides.
Let's see , everyone else has had a shot (lol) now it's my turn, I'm guessing on the caliber but I'm gonna say 58, it looks like it's in unfired condition like it was dropped, like you were seahching an old camp
just a little info, this bullet in particular was not a musket bullet. muskets had round balls. this was a carbine bullet (ex - 1860 spencer carbine, and 1860 henry rifle)