I thought I'd post my "balls" as well-
I've had them for a number of years, but never posted them as I wasn't positively sure they were really stone cannon balls. Over the couse of years, I decided to approach them from a different angle, basically ruling out what they were not! I know they aren't Native American game balls for play, as they are perfectly smooth and larger than the typical Indian ball. They are not stone mill balls because THERE ARE NO SUCH THING! Yes, there were iron mill balls that are confused with iron cannon balls, but the only stone grist tools were stone wheels (I've done a lot of research, but if I'm wrong, let me know!). I don't buy that they were simply some hoddyist's project, because they are made from plain granite and creating them would have been very time-consuming! And they are not to my knowledge Victorean 'garden balls' as the ones I've seen of those are smaller and not perfectly smooth. Mine are about the size of a baseball or slightly larger. I've seen pics of very similar cannon balls dating from around the time of the English Civil War ca, 1650's.
Stone cannon balls became obsolete in the mid-17th century when used against castles and stone forts. They continued to be used, however, in the maritime setting. Stone balls fired ship-to-ship would tear holes through the hull, creating a shower of stone shards and wood shivers. By the time of the early 18th c, ship's hulls became thicker and the stone cannon balls were no longer viable.