That is not a cannonball. It's likely a high school shot put, which are commonly 12 pounds. The screw hole gives it away, as does its machined finish, and the fact that it is steel. The screw hole opens to an inner cavity that allows it to be filled to adjust weight.
Civil War cannonballs were all cast. Most were cast iron, some were lead. There is always a sprue cutoff mark, a mold seam, and a vent hole cutoff mark.
Here is a pretty good treatise on cannonballs vs. outright fakes, and other objects often mistaken as cannonballs:
SolidShotEssentialsMod