From the NYT:
Tell me about the first time you saw a T-shirt cannon. In 1996, I was at a San Antonio Spurs game, and their mascot had one. It looked like it came from World War II — so big and bulky. I thought: Oh, my gosh, I’ve got to have one of those. I bet I could build one. So I went home and called up a friend of mine who was a welder, and by the end of the day we had a cannon that would fire about a block away.
A block!?
Not Unreasonable 