Well if you pump enough compressed air into the air compression one they go pretty fuckin far. I remember had one up to around 200 psi and it cleared a footy field.
Yup... i've built/own both compression and propellant based types, and a half decent compressed air cannon will always come out on top, and they're more reliable. PVC does the trick fine... first one I built for a physics project, a fairly large but portable one, could shoot a golfball out of sight at 60 psi. I built a small-calibre sniper rifle style for a friend, and it was fucking deadly... at 80 psi with a glass marble, it put a small hole in the side of a metal truck compartment wall. Not that I condoned, nor was I present, it managed to send marbles and AA batteries through sets of car and payphone windows at a mere 40-50 psi from 10 or so metres away... considering the max pressure rating for the pipe, from memory, was 240 something psi (but I'd never run them above 120), a well build air cannon packs a lot of punch, typically more than a propellant cannon of similar size, minus all the extra noise, reliability, and cleaning issues.
I can highly recommend investing the extra time/money into using a solenoid valve firing mechanism, rather than a ball valve. Faster air release, and you can even mod solenoids to work without electricity.
All this is getting me in the mood to bring my beast back into commission (it's been years since I've used it, so I'd wanna completely replace all the air chamber piping, keeping my kick-ass modified solenoid).
EDIT: As far as sealing in a BBQ lighter or spark plug for propellant based cannons, or sealing a tyre valve for a compressed air cannon... use epoxy/Araldite!