Hi 'Nando,
I am afraid I've never seen or come across a cannonball of such unique shape - ovoidal!
What practical sense could it possibly have made?
Fitting and rotating in a cannon barrel? No way, I would say.
The only use I can think of would be throwing it from a catapult but then we would have to seek its "date of birth" in the 14th and 15th centuries.
Highly interesting piece anyway and one of the unsolved riddles in historic weaponry ...
Thank you for sharing this, and I do hope for some brainstorming from our members!
Best wishes from a completely stumped
Michael