Help me build the perfect potato cannon?

Question

Gonna build a potato gun combustion cannon out of pvc, but I wanted to make some improvements on that of my friends'. Tell me what you you think, help me decide. Here are my suggestions:

1. Short barrel vs. long one- If the barrel of the gun is short, about 2 feet, will the gun be more powerful? I heard this is why people use (illegally) sawed-off shotguns.

2. Larger combustion chamber? If it can hold more fuel, will the potato go farther? Also, if I fill it with the same amount of fuel as that of a regular sized cannon, will it not shoot as far, due to less pressure?

3. What method of igniting the chamber works best? I'm not sure about matches/lighters, and flints can be a pain in the ***. Are there any other ways to light the gun?

Thanks guys.

Answer 1

There are plenty of instructions on the internet, just Google "Potato Cannon instructions". There are many variations to this cannon, so have fun and experiment, but be safe and smart!

The volume of the combustion chamber is proportional to power of the shot, but a long chamber produces an inefficient compression wave so keep the combustion chamber short and fat.

Muzzle-loading firearms make use of "wadding" - patches of cloth to wrap projectiles to form a good seal with the barrel. The same concept can be applied to potato guns if other misc ammunition is used which does not lend itself to the "cookie-cutter method". The possibilities are endless.

The longer the barrel, the longer the force of the combustion will accelerate the projectile. Too short of a barrel will rob the gun of power. However, if the barrel is too long, the expanding gasses begin to lose pressure and friction of the projectile in the barrel begins to slow it down. Find the optimum length for your own configuration by trial and error.

The initial ignition in the combustion chamber should be close to the center of the chamber cavity for the formation of an efficient compression wave to transfer the energy of the explosion.

Too much propellant gas is as bad as not enough. If too much oxygen is displaced then ignition will not occur. Trial and error will teach the optimum amount of propellant to use in your individual design.

A s***w inserted into the barrel where it connects to the combustion chamber will prevent the ammunition from being rammed too far and falling into the chamber.

Try new ammunition! Potatoes are plentiful, but if you live near a walnut tree...

If something needs to be sealed shut, use duct tape. It starts out as tape, but after you use the cannon the adhesive turns into a very sticky glue that keeps stuff closed.

If your local hardware store does not have the exact fittings listed, don't worry. You will probably be able to find a way to use multiple parts (i.e. reducers, couplers, etc.) to accomplish what the parts listed do.

If you have never worked with PVC before, buy some scrap PVC and a few cheap couplers so you can practice gluing before you build your launcher. Twist each glue joint a quarter-turn as you are pushing it together.

Make sure not to use Christy's glue, it often fails and requires you to work fast. Plan carefully and be ready to move once you apply the glue.

Read the valve's directions to get maximum flow through the valve. This often involves turning a k**b or a collar on the valve.

Follow the directions on the glue, and glue liberally on both the pipe and the socket. Do not use glue or plumber's dope on threads; wrap male threads in a couple of layers of Teflon thread-sealing tape.

Pipe terminology is often confusing. Here are a few abbreviations used: FIPT - Female Threads; MIP - Male Threads; SOCKET- a slip socket; SLIP - unthreaded pipe, use glue to secure in a joint; SPIGOT - male slip on a bushing, etc.; OD - outside diameter; ID - inside diameter (PVC pipe measurements is usually measured by ID, so the OD will be larger than 2")

After cutting pipe, remove the burrs with sandpaper or a file.

Answer 2

in a lot of place potato guns are illegal