Home-Made Artillery: The Spud Gun Quiz

Answer: It depends on where you are.

According to the Bureau of Alcohol, Tobacco, and Firearms (ATF): "...these devices, as described, are NOT firearms provided that they are used solely for launching potatoes for recreational purposes...". In other words, as long as you're not using a spud gun for a destructive purpose, it's not considered a weapon.

However, some local state, county, and city ordinances do consider spud guns illegal. It's your own responsibility to find out what the laws are where you live. Of course, regardless of the local laws, if you're caught using a spud gun in an unsafe or irresponsible way, you deserve all the trouble you're going to find yourself in.

Answer: Hydraulic gun

A pneumatic gun is a cannon powered by pressurized air or CO2. A combustion gun is a cannon powered by the ignition of a fuel-air mix. A hybrid gun is a combination of the pneumatic and combustion cannon, pressurizing the fuel-air mix before ignition. I suppose a hydraulic gun design is possible (though impractical) to make, but you'd probably end up shooting more water than vegetables.

Answer: Firework fuse

The piezo-electric BBQ ignitor is very common, as it's cheap and easy to install. It's not very reliable though. The camera flash works well, and can be salvaged from any disposable camera. Surprisingly, these suckers carry a heck of a jolt, so caution should be used with this method. The stun gun is my favorite ignition source. If wired right, you'll get a strong spark and a reliable fire every time.
A firework fuse might work, but restringing it between fires could be a nightmare. Plus, there could be safety issues. A bad idea.

Answer: Oxyacetylene

Certain brands of hairspray work well as fuel, but they tend to leave residues that can gum up your chamber. Propane and starter fluid burn pretty clean and are very effective. I prefer propane, because it's cheap and easy to meter. Using oxyacetylene to shoot a potato is dangerous and just plain stupid. Every so often, I hear about someone who has a great idea for using the stuff, taking "proper precautions" and "extra safety measures".

The fact is: acetylene doesn't just burn, it detonates. It releases its energy so fast that the shock can easily destroy your gun, and whatever hand happens to be holding it.

It's a stupid risk. Don't do it.

Answer: Piston valve

It's all about air flow. The important factors here are how wide your valve opens, and how fast it opens. Automatic sprinkler valves are popular because they can be wired to open with the push of a button. Unfortunately, they don't open very wide (maybe 1/2 inch), and they're designed to open slowly. Ball valves have to be opened by hand (slow), and also don't have a very big aperture. QEVs are what is generally used in paintball guns, and they work well if you can find one that's big enough. Two inch is the biggest I've seen, and it was pricey.

A piston valve is home-made and built into your gun. It slams open fast and wide, and is well worth the extra time and effort.

Answer: Blowgun

A check valve is a bad idea, as it opens automatically when a certain pressure is achieved. You might not have your gun aimed in time, so it can be a safety hazard. A drain cock would be very awkward to use, and would probably vent too much air, stealing pressure from your fire. Ball valves are sometimes used as a pilot, and they work just fine.

They can be clumsy to operate though. A blowgun works sweet, and being a trigger operated tool, it is ideal for most spud gun designs.

Answer: DWV pipe

Pressure rated material is designed to contain the PSI that you'll be charging your gun with. Steel and brass pipes are more than up to the job, though they're probably heavier than you want. Sch 40 PVC is the pipe of choice. It's easy to cut and solvent weld, and is relatively inexpensive. Check to make sure it has a pressure rating printed on every length. DWV is NOT acceptable for a pneumatic gun.

It's nothing but drainage pipe, and cannot withstand any significant pressure. Also to be avoided is anything that says "cellular core". Using flimsy material is a good way to turn your spud gun into a shrapnel grenade.

Not good.

Answer: All of these.

Better safe than sorry. The hybrid gun can produce huge pressure, that SCH40 PVC cannot contain. You do not want this sucker to pop. A remote ignition system is a good idea, because you just never know. If your gun fails, you do not want to be holding it on your shoulder. And any more than a 4x fuel air mix can cause detonation and huge pressure spikes, the shock of which can rupture ANY plastic pipe, and maybe compromise metal.

Answer: More than 1200 ft per sec

More than 1200 feet per second?! Some of you science buffs probably know that at about 1125 FPS, you achieve Mach 1! Which means that with this monster cannon, you can blast a spud right through the sound barrier (and any cinder block wall that happens to get in the way)! That's cool, man.

Answer: All of these

All of these and more! Confetti sprayers, sniper rifles, baseball pitcher, pyrotechnic effects, etc. With all kinds of different features, like breech loaders, chamber fans, on board fuel supplies, rifled barrels... Spudding is a hobby for those with imagination and creativity, a basic understanding of science, some patience and caution, and a love of things that go BANG!