i'll talk to one of the mechanical guys and see if we can get some drawings out on the internet (they lock me in a dark closet and make me write code all day). As for the exploding part, the only part of the cannon that holds pressure is the air tank on the bottom of the barrel, i'll see if we can get that replaced with a safer material, all other valves, pipes, ect. are metal.
Video:
http://www.youtube.com/watch?v=0cHf3iY4h9k
sorry the video isnt that great, we finished the cannon right before build season. the website isnt quite up to date either.