I'm just starting to get involved with a golf ball firing mortar (1.75" bore).... I've wanted a cannon for years and this is probably as close as I'm going to come in this lifetime. Don't have a suitable base built yet, but have fired it a few times by sandbagging the barrel in place.
Ran across a "cannon ball" fishing weight mold that will cast a 1 pound 1.700" ball. Since I quit the cowboy shooting stuff (spend 6 hours out at a range and actually pull a trigger less than 15 minutes) I have a lot of wheelweights in buckets outside of the shed just asking to be cast into mortar rounds.
Lotsa fun !!!