As mentioned above we need precise measurements to correctly id you bullet. It could be anywhere from .32 cal up to .44 cal depending on the size of your fingers. It looks unfired to me, in that I don't see any rifling marks in the photo, and it doesn't seem deformed at all, and from the patina I would say pre 1900. My knowledge is more toward modern post 1900 ammo, but there are some people here who may be able to look at it and know exactly what it is. Maybe CannonballGuy will see this thread.