Potato Cannon (Early 2006)

Early in 2006 a friend and I decided we needed a potato cannon. We did some research on the internet, scrounged up some materials, and bought a few things from the local hardware store. Pretty soon we were launching spuds out of sight.

Our potato cannon is made of schedule 80 PVC pipe and has a combustion chamber that is 3" in diameter by 18" long. Our barrel is 1.5" in diameter by 4' long. That gives us a chamber to barrel ratio of 509:340 which is really close to the 1.5:1 ratio we'd read was most efficient. Obviously, we could make the chamber as big as we wanted to and get even more power, but there comes a point where the returns are too small to measure and much more propellent is required.

We had to buy a 3" to 1.5" reducer, threaded cap, and BBQ igniter from a local hardware store. Then, we PVC cemented everything together and left it to dry for a day. We then drilled two small holes near the back through the dual layer of pipe for two bolts wired to our BBQ igniter. These bolts have two nuts apiece so their depth into the chamber can be adjusted to get a good spark gap.

Trunk Loaded With Guns
After a fun day of plinking, airsoft, and giving spuds the ride of their life

Shooting potatoes into the air was fun for about two minutes, then we started looking for slightly more destructive things to shoot. A wad of newspaper with a handful of rocks turns it into quite a large shotgun. You can fill the barrel with sawdust for an instant confetti parade. An old lawnmower axle will punch a hole through the side of a scrapped truck. It's also fun to shoot glowsticks at night; they look like tracers. Shooting bags of kerosene at bonfires is also entertaining. However, it's not a good idea to shoot a hunting arrow straight up in a field because there's nowhere to hide. We were quite scared when that thing came down 10 feet away with a resounding THWACK!

Potato Gun Shooting Clay Target
Shotgun mode on a clay pigeon

Eventually, I got the idea to make some dedicated wooden bullets for the gun. I made these out of oak on a lathe, and they fly very well. I use ducktape fins so they can be easily replaced when they become too shredded. I shot one straight up and it took nearly 12 seconds for it to come back down. That works out to an altitude of around 575 feet. They will easily go through roofing tin, and even a trash can lid.

Wooden Potato Gun Bullet
Wooden Bullet. 1.5" diameter


Shot Up Tin Roofing
What it does to old tin roofing

Failures
The gun has only failed on me twice, and no one was hurt either time. The first time was soon after we'd made it when we'd rammed a really tight fitting potato down the barrel. When we hit the igniter, the gun fizzled and sounded like a rocket about to take off. Hot flame burnt through the threads at the back and caught the pipe on fire. After putting it out we simply cut off the destroyed fitting and then cut down the barrel to maintain the 1.5:1 ratio. That reduced our gun from 6' to 5.5'.

On January 1st, 2009 the potato gun came apart on me. We had loaded it with around 100 empty .22 shells and a dozen empty 12 gauge hulls to shoot at a clay pigeon. I shot, and the barrel came off the combustion chamber. I simply cemented it back together and it's as good as new. I think I would have broken the target had the gun not come apart ;D



Future Upgrades
-Make a better trigger
-Convert it to run on propane
-Build a streamlined wooden bullet and find the maximum range the gun will shoot
-Mount the gun on a swivel on my canoe and go marauding




I'll have a video of the gun at some point; I need to get more material though.