Potato cannon

A potato cannon (sometimes known as a spud gun, not to be confused with a toy of the same name) is a pipe-based cannon which uses air pressure (pneumatic), or combustion of a flammable gas (aerosol, propane, etc.), to launch projectiles at high speeds. They are built to fire chunks of potato, as a hobby, or to fire other sorts of projectiles, for practical use. Projectiles or failing guns can be dangerous and result in life-threatening injuries, including cranial fractures, enucleation, and blindness if a person is hit.

The potato cannon can trace its origin to the World War II-era Holman Projector, which was a shipboard anti-aircraft weapon.

All spud guns propel projectiles down their barrels using pressurised gas in the same manner as a firearm (although at a much lower pressure). There are four basic ways that spud guns may achieve this:

Combustion powered spud guns typically have the least complex designs, the four basic elements of which are:

In order to fire, the operator loads a projectile into the barrel, adds fuel to the combustion chamber (for example aerosols or propane), and triggers the ignition source (often using a piezoelectric barbecue igniter). The fuel then ignites, creating hot expanding gases, and forcing the projectile out of the barrel. Distances vary greatly depending on many factors, including the type of fuel used, the efficiency of the fuel/air ratio, the combustion chamber/barrel ratio, and the flight characteristics of the projectile. Common distances vary from 100 to 200 meters, and there is a reported case of a cannon exceeding 500 meters of range.

Advanced combustion launchers may include metered propane or calcium carbide (acetylene) injection to ensure proper fueling, chamber fans to mix the fuel with the air and accelerate venting of the chamber after firing, multiple spark gaps (spark strips) to decrease combustion time, and high-voltage ignition sources (flyback circuits, stun guns, camera flashes, etc.).

Combustion launchers are usually less powerful than their pneumatic or hybrid counterparts, especially when hairspray / alcohol is used as a propellant. Bottled oxygen can be added to the firing chamber, though this can cause an explosion of the pipe when firing, potentially injuring anyone nearby.

...
Wikipedia