Try matching it up on this chart so graciously posted by TheCannonBallGuy.
[FONT=Verdana,Arial,Tahoma,Calibri,Geneva,sans-serif]http://www.civilwarartillery.com/shottables.htm
I don't see where it would fit, I know nothing about them.
My thinking is it is for some other use like A2cions said.
Welcome to TNET and hope you will tarry with us and share stories and pics of finds! I am sorry to say but I agree that it is not a cannonball. From the damage and the overall appearance, the ball appears to be Steel and is likely a very large bearing.