I don't know how the kid survived it i guess they where just using compressed air he got lucky because when i was a teen we used hair spray for propelant and a frozen tater it would dent steel dumpsters haha but none where dumb enough to look down the barrel what a dumb arse kid.
they are easy to make, i use this method barrel half the width of the chamber and twice as long. so a 2' 4" chamber would have a 4' 2" barrel. then i use a bbq lighter attached to nails with a hose clamp around it so the nails can't come out. nails create the arc hairspray creates the boom