A potato gun (also called a spud gun or potato cannon) is a DIY launcher that uses either combustion or compressed air to fire a potato projectile. The combustion type is the most popular for home builders because it’s simpler and cheaper to construct, typically built from PVC pipe fittings, a fuel source, and a spark igniter. Before you start, check your local and state laws. Potato guns are classified differently across jurisdictions, ranging from unregulated toys to destructive devices.
Combustion vs. Pneumatic: Two Main Designs
Combustion potato guns work by igniting a flammable gas inside a sealed chamber. The rapidly expanding gases push the potato down the barrel. Pneumatic designs use a tank of compressed air released by a valve. Both get the job done, but the tradeoffs matter.
Combustion builds are simpler. You need a chamber, a barrel, a fuel source, and a spark. There’s no air compressor, no pressure tank, and no valve assembly. That’s why most first-time builders go this route. The downside is inconsistency. Your shot power varies depending on how much fuel you spray, how well it mixes with air, and ambient temperature.
Pneumatic builds are more complex and expensive but far more consistent and powerful. You control the exact pressure in the tank before each shot. However, they require a reliable ball valve or piston valve, an air compressor, and careful attention to pressure ratings on every fitting.
How Fast Potatoes Actually Travel
The speed depends heavily on your fuel choice. Research using high-speed video to measure combustion-driven potato cannons found a wide range of muzzle velocities across five common fuels. Acetylene performed best at an average of 138 meters per second (about 308 mph). Methanol came in second at 48 m/s (107 mph), followed by butane at 35 m/s (77 mph), ethanol at 33 m/s (75 mph), and propane at the bottom with 28 m/s (62 mph).
For context, even the slowest propellant on that list launches a potato faster than a professional baseball pitcher throws. Acetylene approaches the speed of a crossbow bolt. These are not toys, and treating them casually is how people get hurt.
Basic Parts and Assembly
A combustion potato gun has three core sections: the combustion chamber, the barrel, and the ignition system.
- Combustion chamber: A wide-diameter pipe (typically 3 to 4 inches) capped on one end. This is where fuel is sprayed and ignited. A cleanout adapter on the back end lets you open the chamber to add fuel.
- Barrel: A narrower pipe (typically 1.5 to 2 inches) that press-fits into a reducer coupling on the front of the chamber. The potato sits at the base of this barrel, forming a seal.
- Ignition: A piezoelectric igniter, the same type found in BBQ grill lighters, mounted through the chamber wall. Two wires inside the chamber create a spark gap of about a quarter inch.
The chamber and barrel connect through a reducer fitting. All joints are solvent-welded using PVC primer and cement. This is not optional. Threaded connections alone will not hold under combustion pressure.
Getting the Seal Right
The potato itself acts as the projectile and the gas seal. For a clean, tight fit, sharpen the inside edge of the barrel’s muzzle end so it cuts into the potato when you ram it in. The key is shaping the edge into an inward-tapering bevel, almost knife-like, so the barrel slightly compresses the potato as it enters. If you leave a flat, factory-cut edge, you’ll get air gaps that bleed pressure and kill your shot. A metal file or rotary tool works for this.
Push the potato down the barrel with a wooden dowel until it seats near the chamber end. Leave no air pocket between the potato and the chamber opening.
Solvent Welding and Cure Times
PVC solvent cement chemically fuses the pipe and fitting into a single piece. It’s not glue. The solvent softens both surfaces, and as it evaporates, the plastic re-hardens into one joint. But the joint needs time to fully cure before it can handle pressure.
For pipe in the 1.5 to 3 inch range at normal room temperatures (60 to 100°F), the recommended cure time before pressurizing is 8 hours. In cooler conditions between 40 and 60°F, that doubles to 16 hours. Below 40°F, you’re looking at 3 full days. Humid conditions add another 50% on top of those times. Firing a potato gun before the joints have fully cured is one of the easiest ways to cause a catastrophic failure.
Why PVC Failure Is Dangerous
PVC pipe is the standard material for DIY potato guns because it’s cheap and easy to work with. It’s also the biggest safety risk. OSHA describes PVC under compressed gas as a material that “literally explodes like a bomb, sending shards of plastic flying several feet in all directions.” Unlike metal pipe, which tends to split or bulge when it fails, PVC shatters into jagged shrapnel.
This happens because PVC is a brittle thermoplastic. It doesn’t stretch or deform before breaking. When internal pressure exceeds the pipe’s rating, the failure is instantaneous and violent. Cold weather makes PVC even more brittle. So does UV exposure over time, sunlight gradually weakening the material with each use season.
Some builders switch to ABS pipe, which is the only plastic OSHA has approved for compressed air systems in certain formulations. ABS tends to crack rather than shatter, making failures less explosive. Metal pipe (steel or aluminum) is the safest choice for the combustion chamber, though it adds weight and cost. If you stick with PVC, never exceed the pipe’s pressure rating, never use acetylene (which generated peak pressures over 600 kPa in testing), and inspect the pipe for cracks, discoloration, or damage before every use.
Fuel Selection and Use
For a standard combustion potato gun, the most commonly used fuels are aerosol hairspray, butane (lighter refill cans), and propane (small camping canisters). Each has tradeoffs.
Hairspray is the classic beginner fuel. It’s easy to find and delivers a consistent, moderate shot. The downside is residue buildup inside the chamber that needs cleaning, and the propellant-to-air ratio is hard to control precisely. Too much fuel actually kills the shot because combustion requires the right fuel-to-oxygen mix.
Butane and propane are cleaner burning and easier to meter. A one-to-two second spray into the chamber is a typical starting point. Propane averages about 28 m/s muzzle velocity, butane about 35 m/s. These are relatively safe choices for PVC builds because they produce lower chamber pressures.
Methanol and ethanol (denatured alcohol and grain alcohol) can also work, delivering velocities around 33 to 48 m/s. Acetylene dramatically outperforms everything else but generates chamber pressures that can approach dangerous levels for PVC pipe. It’s best left to metal-chambered builds or avoided entirely by casual builders.
After spraying fuel into the chamber, seal it and wait a few seconds for the fuel to mix with the air inside. Then fire the igniter. If you get a click but no bang, the mix is probably too rich (too much fuel). Open the chamber, fan it out, re-spray with less, and try again.
Maximizing Performance
Three variables control how far and fast your potato flies: chamber pressure, barrel length, and projectile weight. Research on combustion cannons found that muzzle velocity increases with the product of initial pressure and fuel gas volume, and decreases with heavier projectiles. In practical terms, this means a lighter, well-trimmed potato plug will fly faster than a heavy chunk.
Barrel length matters too. Pressure measurements show that for most fuels, chamber pressure peaks within the first foot of the barrel and then either stabilizes or drops. A barrel that’s too short wastes expanding gas. One that’s too long adds friction that slows the potato after the pressure has dropped. Most builders find that a barrel between 3 and 4 feet gives the best balance for combustion designs.
A fan or mixing device inside the combustion chamber can also improve consistency. Some builders install a small computer fan to circulate the fuel-air mixture before ignition. Better mixing means more complete combustion, which means more pressure and less wasted fuel.