> After reading about Eric's potato gun, I sat here and wondered how many people might try to make one and get blown up. There are a few cautions. If you are not a southerner, do not try this at home. Even if you are a southerner, be sure that you don't put too much stuff in there at one time. One spud (I've always called them "spud cannons.") will go twice as far as two. Three or more may cause the gun to explode.
> Heavy objects, like a can of soup or a rock, have too much inertia and the pressure builds up too fast in the combustion chamber. It could boom out the wrong end. Don't experiment with fuels. There are some common combustables out there that will end your day quickly.
> A safer projectile is a tennis ball. It has a higher mussle velocity, but shorter range. This is due to the low mass and higher air friction. The trajectory is different from a spud, because it tends to fall straight down after it loses its initial speed. Another advantage is that it's a lot less fun being hit by a falling potato. A tennis ball will only hurt at short range, and if you use a high angle, that shouldn't be a problem.
> Most cities have laws about discharging a fire arm in the city limits. The definition of a "fire arm" easily fits a spud cannon.
> I don't recommend these homemade weapons, but I have to admit that they are pretty exciting at night. Forget the potato and you can enjoy a fireball big enough to bring the cops.
> One more thing. If you insist on experimenting with spud cannons, don't forget to yell "Hey, y'all, watch this!" before igniting the charge.
> How"famous last words"ard

Hmm. I just read Erics description of the "spud gun".

A different (and possibly better) version is the PAC-2 (pneumatic air cannon type 2). You take two pieces of PVC, one smaller than the other, stick the appropriate size fitting on the end, and screw both pipes on to an electric sprinkler valve. On the larger pipe, you put an end cap with a standard air valve in it, the kind that you see on car tires. Duct-tape three 9 volt batteries together, and wire them up to the sprinkler valve. Put a switch or button somewhere in the circuit for a trigger.

That's it for construction. However, one problem with this type of spud gun is that it requires an air compressor. If you don't have one, you might be able to get by with a foot pump, although I don't know if you can get the required pressure with one. If you have a compressor, connect it to the tire valve, put about 60 PSI of air in there.

The tricky bit with this is that the projectile has to at least semi-fit in the barrel. Since it uses air pressure to fire, irregular objects won't work too well. The air passes around/through them. You can work around that by shoving your projectile inside of a plastic cup. My brother found that he could make a paintball shotgun simply by putting a few paintballs in a cup and firing it.

So get your projectile, shove it down the barrel, and flip/press the switch. If the 9V batteries are charged and the sprinkler valve is functional, the gun will make a loud POP, and send your projectile flying.

The instructions are a lot longer than the explosive-powered version, but the gun and projectile can be reused (just pump more air into the gun), and the chance of it exploding are just about nil.

- Atha"Balloons don't work too well"leon