Potato cannon

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

[6] Combustion powered potato cannons 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).

[8] In order to fire, the operator first readies the pressure-triggered valve then injects several times the normal amount of fuel and appropriately more air.

[16] It is rare for a potato cannon to be powerful enough to break the sound barrier, although there are some cases of this happening using specialized designs.

Projectiles or failing guns can be dangerous and result in life-threatening injuries, including cranial fractures, enucleation, and blindness if a person is hit.

A pneumatic potato cannon
A large pneumatic design: The projectile is loaded in the muzzle (not pictured), which is then attached to the cannon (at 2). The air reservoir (3) is filled to 120 psi (0.83 MPa) using the Schrader valve (4). Upon opening the solenoid valve (1), the air from the reservoir is transferred to the projectile, which is fired out of the muzzle.
PVC dry ice cannon in use, 1.5kg (3 pounds) of concrete is poured at the bottom to reinforce it, and plastic sleeves are used to stiffen the lower (highest pressure) part.
A typical propane gun bird scarer