My fraternity had a cannon we shot at football games (and occasionally at a bush party). Perfect diameter for a pool ball. Don't ask me how I know. That muzzle loader was the 2nd one we had. The HOWITZER we had was stolen allegedly by a rival frat and dumped in the Ouachita river.
We have a neighbor with a cannon in the neighborhood we live in off Hwy 30. He posts on Nextdoor when he will be shooting it off. Usually at least once on NYE.