I've built a couple of those. They are definately fun. The chamber started cracking on my first one so I built another one. Currently the cap is stuck on (dont use hairspray as a propellant, its sticky). I've tried everything I can think of to get the cap off. My only other option is taking it to the plumbing store and having them do it I think.
Its fun shooting a potato through a chain link fence. It makes french fries
