More About Air Cannons and Potato Guns

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POTATO GUN FAQs

Many of you have been asking if I still use my potato guns. Hell Yes, every chance I get, but finding an adequate and safe launching place isn't easy. The following is a list of frequently asked questions regarding potato guns and potato cannons.

What is a potato cannon or potato gun?
What are potato guns made of?
Are potato guns dangerous?
What are the legal implications?
How easy is it to build a potato gun?
What does it cost to build a potato gun?
What is a combustion potato gun?
What is a pneumatic potato gun?
What are the advantages to each?
Can I use DWV pipe or cellulose, even though it says not for pressure?
What does PVC stand for?
How does PVC differ from ABS? Which is better?

POTATO GUN HISTORY

No one knows who started them. Legend states they originated from tennis ball cannons made from pop cans and lighter fluid, back in the 50's. They come by many names, spudzookas, PVC mortars, potato guns, spudguns, potato cannons. But they are all the same thing: an array of plastic pipe which propels a projectile, usually a potato, at incredible speeds, by means of combusted gas or compressed air. They can also be used for more practical purposes, i.e. line throwing.

CONSTRUCTION

Potato guns are made out of Schedule 40 PVC pipe, the plumbers standard. They are NEVER CONSTRUCTED from DWV (drain, waste, vent) pipe as it is not meant for pressure and the resulting effects if pressurized could be deadly. It is thick and durable and has a great pressure rating to around 300 psi, so it is safe for minor 100 psi launches. Another method of construction is using ABS pipe, another durable type. I do all my shopping at the Home Depot. They have an excellent selection of every kind of pipe and connector, and their prices are very inexpensive. Radio Shack supplies all the electronics. Valves and hose clamps (for support) can be found at auto stores.

DANGER

Like anything device created to launch something, potato guns are dangerous. They propel projectiles at high velocity, and thus you don't want to get hit by one or point them at windows or other important things such as cats. And when you shoot things like ice or wood as opposed to potatoes, they have much more mass and become even more dangerous, considering they do not vaporize on contact.

Combustion cannons use a flammable propellant and thus have a danger of exploding or fire, however this is rare if proper methods are used. Compressed air guns can be regulated to within the limits of the PVC pressure rating but still risk rupture or blown valves, however the usual pressure of 100 psi is well within the limits of the pipe. Combustion cannons can send the endcap of the pipe shooting off, and they can shoot large flames from the barrel. But they are generally safe when used with precaution and common sense.

LEGALITY

Legality is a sketchy issue. All seem to agree they are novelty devices, for amusement only. For all intents and purposes, they are a recreational device which shoots small projectiles at stationary targets. Obviously, you don't want to go shooting small rodents out, or billiard balls at billboards, but for the most part there shouldn't be a problem. Combustion cannons may cause a noise problem however. I advise you check with your state and local law enforcement agency for further information. The following is a letter that finds its way onto most potato gun sites about legality. I cannot vouch for its validity, however.

============================================================================ 
 
DEPARTMENT OF THE TREASURY
Bureau of Alcohol, Tobacco and Firearms
Washington, DC  20226
E:CE:F:TE:RAT
Sep 12 1995                   3311.4

Mr. XXXXXXXXX
address...
City, State  Zip

Dear Mr. XXXXXXXXX
This refers to your letter of August 18, 1995, in which you ask about  the legality of a device known as the "Spud Gun."
These subject devices are generally constructed from PVC tubing and fittings and are designed to launch a muzzle loaded potato using aerosol hair spray or other type of propellant.  Ignition is by means of some type of "spark" igniter.
The Bureau has previously examined devices known as "Spud Guns, Potato Guns, or Spudzookas" and have determined that such devices, in and of themselves, are not firearms as defined in Title 18 United States Code (U.S.C.), Chapter 44, S 921(a)(3) or 26 U.S.C., Chapter 53, S 5845.

However, any similar devices which can be determined to be weapons by reason of their design construction, intended use, actual use, ammunition or other factors may meet the definition of a firearm under  Title 18 or 26 U.S.C.
We suggest that you contact your State and local law enforcement authorities concerning possession of such devices.
We trust that the foregoing has been responsive to your inquiry.  If we may be of further assistance please contact us.

Sincerely yours,
Edward M. Owen, Jr.
Chief, Firearms Technology Branch

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SKILL

Building these can be fun, but the skill needed is advanced. You need a working knowledge of mechanics, hardware, construction and physics to know what you are doing, and it is good to know simple electronics for the triggers to some guns. Many young (16 or younger) people ask me about these, often for science projects, and I always advise them to consult an adult first. It's also a great bonding experience. You can get your Potato Gun Kits here.

Simple tools are all that is necessary. For more advanced guns, dremels or hacksaws may be necessary. Make sure to use proper ventilation when gluing and priming. Soldering electric components also takes some skill. Other launchers exist which are vastly more complicated, requiring more skill. You can get your pre built potato guns here.

COST

Building a cannon is a relatively inexpensive hobby. Most PVC pipe ranges from $2 to $6 for 10 foot sections. Joints and connectors are around $0.39 to $4 for large pieces. Glue and primer are about $3 each. Valves run from around $8 for good ball joints to $12 for electronic sprinkler valves and larger brass ball valves. Electronics run around $12 for all the necessary switches and components. All in all, expect to spend around $30 to $40 to make a good gun. Prices go higher as the diameter and size of the gun increases.

 
COMBUSTION SPUDGUNS

Combustion cannons have a large chamber which reduces to a smaller diameter pipe, from which the potato is launched. Combustion is achieved by spraying in a propellant, usually hairspray. A flint or electric lantern igniter is used to generate a spark, which ignites the gases, propelling the potato, which can exit the barrel baked.

PNEUMATIC SPUD CANNONS

Pneumatic cannons are completely different, and thought of as much safer and more powerful. These cannons have two chambers, one in which air is compressed, and another in which the projectile is shot. Between these two chambers is a diaphragm, or a valve of some sort. When the valve is opened or the diaphragm flexed, massive amounts of high pressure air force the potato out.

DIS/ADVANTAGES

What are the advantages to each cannon?

DEATH

DWV pipe (drain, waste, vent) and cellulose pipe are both marked NOT FOR PRESSURE. This means DO NOT USE THEM OR PRESSURIZE THEM AT ALL. This topic came up in the mailing list. These pipes can tolerate no pressures and will explode if pressurized, causing great harm or death.

POLYVINYL CHLORIDE.
PVC stands for Polyvinyl Chloride. Here is a link to PVC pipe statistcs and its applications: PVC FAQ.

ABS VS. PVC
The debate continues as to which pipe is better. I personally use PVC; this is only because I have not tried ABS yet. I am told ABS is stronger and cheaper, but I suggest you do your own research.