I built one out of PVC pipe last summer with some friends. We bought everything at home depot, even the barbeque igniter on 5 feet of wire for remote firings. The guy at the checkout totally knew what we were up to.
We used PVC cement to gule the pipes together, but watch out when using that shit cause its hella flammable (my friend couldnt wait to test it, and had flames come within inches of his face). Our chamber was really big, and had a screw on attachment at the back so you could fill it with hiarspray, screw the cap on and fire it. The thing sounded like a howitzer, and could launch a smallish potato about 2000 feet. Eventually it broke though when we put too much hiarspray in it and blew off the screw cap, which hit my house. Fuuuuuuun times though.
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Rowen
'Aren't you Buzz Lightyear?'
*whispers* 'I love your movies!'
'URAAAAFWAAAGAAA!!!'