Ruger -- Could be a lot of things. Without seeing it and weighing it, there is no real good answer for you. I know since I have been into relic hunting, I've seen a few things folks thought were cannonballs that weren't. One of the most common mistaken things, are the round ball things that go on a gate or fence...don't know what they are called but they look like a cannonball but are no where near the weight.
The main weights of them are going to be 6, 8, 12, and 24 pounds. "Solid shot" ones won't have threads or a zinc or brass fuse in them. Now it could also be a "grapeshot" which would be smaller than a 6 pound ball, but weigh only 2-3 pounds or so.
And another common thing, especially for in areas where they mined, are what they call "ore crushing balls". And all they did, was exactly what you think by the name...they crushed ore by being dropped over and over repeatably. They'll usually be found with LOTS of dents and dings in them.
