Potato guns are lots of fun. You can shoot things and destroy stuff. However, a regular potato gun can explode due to its PVC construction, expensive due to the large pipe fittings and loud because it is so large. Our mini potato gun is much safer due to its steel construction and compressed air power source.
Step 1: Safety
This mini potato gun is dangerous! DO NOT use hard projectiles like steel balls or batteries, as these projectiles can bounce off things and hit you. Never exceed the working pressure of any component. DO NOT use PVC pipe or any pipe not rated for compressed air. Use of PVC pipe may cause an explosion, resulting in serious injury or death. PVC pipe is only allowed if it is on the barrel, after the main valve. NEVER look down the barrel, even if unloaded. ALWAYS treat the mini potato gun as if it were loaded. ALWAYS use eye protection. ALWAYS wear ear protection if you are using pressures above 200 PSI and/or dense projectiles.
Step 2: Tools and Materials
NOTE: All parts should be available at any hardware store, except for the air compressor tank valve (also sold as pipe thread tire valves) which can sometimes be found at an auto parts store. Galvanized pipe fittings may be replaced with black iron or brass, but galvanized is usually cheaper. Bell reducers (also known as reducing couplings) may be replaced with a pipe coupler and reducing bushing. I have included links to an online source for these parts, but usually local stores have better prices. I built this mini potato gun using spare parts I had lying around, so you may substitute parts that you have access to as long as they fit and are rated for the pressure.
Ear Protection (if using potatoes or other dense projectiles)
Bike pump capable of at least 100 psi
2 pipe wrenches (vise-grips or channel locks work too)
Step 3: Assembly
Wrap high density Teflon tape on all the male pipe threads. Make sure to do three overlapping clockwise wraps. Using your two pipe wrenches, tighten all joints until snug. BE CAREFUL to not overtighten the little 1/8" tank valve. Make sure you install the ball valve so when it is closed, the handle is pointing towards the air tank valve. Look at the picture and the CAD diagram for help. You can customize the air cannon by using a longer steel pipe nipple for the air tank or a different size pipe for the barrel.
Step 4: Shooting
Remove the protective cap from the air tank valve and hook up your bike pump. Shut off the ball valve. Load your ammo and pump up your potato gun. I usually pump mine up to 150 PSI. Aim at your target and quickly open the valve to fire. Shut off the valve, load more ammo and pump up the potato gun again to fire again.
Mostly safe (Eye protection required)
Wet toilet paper (you can also load this first then load a loose fitting projectile)
A little dangerous (Eye protection and earplugs required)
Potato (Get a spare 1/2" grey SCH 80 PVC pipe nipple and sharpen one end to cut potato slugs)
Deadly (never do)
Other hard, dense projectiles that are unlikely to break apart