I'm no expert, but its obviously a large caliber round, and there for, probably was shot out of a black powder rifle.
Are there grooves along the sides where the rifling cut into it? if there is then i was probably shot from a breech loader and from the looks of the bullet, it was shot from a self-contained cartridge.
however if its not it may have been shot from a musket. Again, I', no expert and its probably going to be very difficult to say exactly what gun and what round, but like i said, probably a black powder breech loader of some sort.
I'm not aware of any round that is bigger than a quarter, that's about 1" isn't it? thats awfully big. Are you sure its a bullet? Is it lead?