How Spud Guns Work

Spud Gun Theory

The two basic types of spud gun -- combustive and pneumatic -- each use a rapidly expanding volume of gas to move a potato. Both types of guns are typically made of PVC pipe, although some people use acrylonitrile butadiene styrene (ABS), aluminum or other piping materials.

All spud guns have the same basic components:

A chamber in which gas reaches a high pressure
A barrel for the projectile
Some type of firing mechanism

Typically, the sharpened end of the barrel acts as a barrel knife, which shaves off the excess potato during loading.

The method for creating high-pressure gas is what differentiates combustive and pneumatic spud guns. "A combustion-based spud gun," says Suprise, "uses a flammable vapor...you have a fuel-air mix in a chamber, and then you have an ignition source, typically an electric barbecue sparker, something of that nature, which will ignite that flammable mix." When the vapor ignites, the resulting explosion creates a large volume of hot gas, which forces the potato down the length of the barrel and out.

A pneumatic spud gun uses compressed air rather than flammable gas. Suprise explains:

You have a large-volume chamber that you pressurize with an air compressor or a regulated CO2 tank or something of that nature, and then a fast-acting dump valve, and then your barrel…when you fire that valve, that dumps that entire amount of air…just in the blink of an eye, sending your projectile down the barrel at great velocities.

In the next section, we'll examine the differences between combustive and pneumatic guns and how each generates the pressure needed to fire the potato.

Spud Gun Materials and Spud Gun Modifications: Breech Loading

Although PVC and other pipe materials are often pressure tested, they are not intended for use in building projectile launchers. People who build spud guns do so at their own risk. They also must take certain precautions, such as drilling holes only through couplings (where the material is twice as thick) to reduce the risk of shattering during use.

Many spud guns are barrel loading. The user forces a potato all the way down the length of a barrel using a pole or rod. However, some designs are breech loading, meaning that the user can open the gun near the chamber and insert the potato there.