anything related to cannons going wrong is welcome, wether it be explosions, misfire, un-expected results, anything goes.
to start off i would like to share 2 time where i have almost lost my face.
first time was with my bigger cannon. it had CO2 setup on it, and was charged to about 80 psi. i had loaded the barrel separately with about 200 airsoft bb's and was screwing on the barrel (inside my room) when i tapped the blowgun. A massive bang follows (it was 2" from my head) and i feel a rush of air, and then bb's ricochet around the room! i now have a 6" patch on my ceiling that looks like a golfball.
the second time was just a few days ago. i had loaded my bigger cannon with a 1" clay ball (plasticine clay) and had it at about 100 psi. i was walking outside with it when i accidentally tapped the blowgun(you would think i would learn

so far my dad hasn't noticed anything.
another story was again with the big cannon, with the CO2 setup on it. the way the co2 was rigged had a high pressure 1/8 ball valve facing toward the ground. i was screwing on the barrel and the gun turned and opened the ball valve. before i could react the chamber was at about 180psi, and by the time i shut it off it was at 200. the sprinkler valve was only rated to 115, so i was expecting it to rip at any second. the positive side was that it made a loud bang when i fired it.