BE careful with these. They ARE considered to be illegal in most areas.
That being said, I have a certain friend that has a pretty extreme interest in all things inolving fire and things that go "boom". His hand held potato guns launch potatos well over 200 yards, and cause severe damage to Pressure Treated wood fences.
Save potatos by cutting them in half. Save the "barrel" by skinning the tators first. And Automotive Ether (Quik Start) is slightly more potent than hairspray and seems to still create minimal pressures that the PVC can withstand...from what I've been told.