Check this.
ANSWER: Hi Kim,
It does appear to be a cannon ball. Given the weight, it may be a hollow one that could still contain black powder and thus it could be quite dangerous. DO NOT PUT IT INTO A FIRE, Throw it, hit it with a hammer etc....
Does it have a plug, either brass, bronze or steel? it would be round, perhaps 1 inch in diameter and conforming to the shape of the ball? If so, this is the fuse! Does it have any numbers, letters or symbols struck into the metal? this could be on t he fuse as well.
The ball is from the civil war time period and was probably cast in one of the steel mills in northern Indiana. I would donate it to the local historical museum, just to get the thing out of the house!
You CAN NOT sell it, you CAN NOT ship it, It is illegal to ship munitions. Since it may still have black powder in it, it is considered hazardous. Do not send the kids to school with it as show and tell.
http://en.allexperts.com/q/Archaeology-654/2010/3/cannonball-4.htm