40what they are good for
Cannonballs are pure decoration now. A placed cannon goes off when you hold a torch to it, so nothing loads these and nothing consumes them. What is left is set dressing: a heap beside a deck gun, a rack in a fort armory, clutter for a pirate ship build.
They stack deep and the Pirate keeps them in stock permanently, so one shopping trip covers an entire build with no reason to ration them. If you were saving them expecting to need ammunition later, stop, there is nothing to save for.