Probably the dumbest thing I personally ever did is: When I was a kid in high school, I made a cannon out of a piece of 1/2” galvanized pipe (1/8” wall at best) a coupling and a plug for the breech. Drilled a hole in it for a fuse and welded three legs and some sights on it in welding class at the high school. Yeah our welding instructor gave me a grade on it....
Used to shoot it with one cap full of goex. Don’t know how much powder that was I would guess 30 grains or so. For projectiles, marbles wrapped in toilet paper. Shot up the whole pound of powder that way. I was at a friends house and we were shooting it across a wash at a hillside when we ran out of powder. His words” my dad has a bunch of reloading stuff in the garage, he has powder.” We loaded it up again with the standard load, one capful. It sounded more like a bottle rocket than a cannon, so we put two capfuls in it. This time it grenaded. We were standing inside the back of the garage watching the hillside out the widow, when it went off. It was LOUD!! We never saw the impact on the hill, I’m sure it vaporized the marble. Blew the plug out the back and took a chunk out of the brick. Hate to admit how dumb I was as a kid. Live and learn I guess...