When I was in high school, we had a 'cannon' behind one end-zone that we fired at football games.
It was basically a piece of 2" pipe, 2' long, welded to a square of 1/2" plate.
We would drop a couple of starter blanks down the pipe and then drop a piece of solid rod that weighed about 8 pounds down the pipe on top of the blanks and it would go boom.
Well, one Friday night it was wet (had rained all day) and apparently water had accumulated in the pipe and everyone thought someone else had emptied the water out of the pipe.
We had pre-dropped a few blanks down the pipe, and when the team took the field, we dropped the weight and.....nothing.
So one of the guys dropped in a few more....dropped the weight...and......nothing.
Yes, you guessed it....our young dumb asses dropped a whole box in and released the weight.
Well.....it finally went BOOOOOM.....and.....like a mortar, the 8 pound weight went about 20 feet in the air, landed right on top of the crossbar of the goal post (like it was scripted), and left a dent that was still there until the goal posts were replaced a few years ago.
One guy went to the hospital with singed eyebrows and a few blisters (the rest of us went to change underwear) and the cannon was officially retired for the season.
