My buddy cut down several single shot 12 ga shotguns to look like an old pirate pistol, and They knew that if I deemed it safe, I'd shoot it. Which I did, but I asked for the rest of the barrel.
I took the barrel to the local Iron Works, where another friend threaded the "breech", put a hex head plug into it and welded it shut, then drilled a hole for a fuse. We then took a scrap piece of 4" channel iron and welded a L shaped piece to the end as a brace for the cannon.We used a piece of the stuff that is used to strap down conduit to hold the cannon in place, and we were set.
I'd put 100 grains of black powder followed by a wad of paper towels, a small handful of 1/4 inch aluminum balls that were used to plug air lines, and some more paper towels. A rather long piece of CVA cannon fuse and we'd light it. This did good for a while, lots of smoke, destroyed brush, and constant stomping out small fires due to the burning wadding. Until one day when we decided 150 grains would be better. When it went off, it broke the L shaped bracket, the barrel slid out from the confines of the clamp, and embedded itself several feet into a bank that was a few yards behind us..
Sooo... I decided that some 7mm Mag brass, some powder, both black, smokeless and perhaps some Pyrodex and a black cat would disrupt some fire ant beds. Put in as much as it would hold and still accept a black cat, squeeze the case mouth with pliers so that the fuse is sticking out , poke it into an ant bed, light and run.
That was one year that the fuses on the firecrackers were mighty fast... but I still have all of my fingers. And was covered by ants more than once.