Been lurking here for a while after discovering this place while doing research on a pneumatic cannon, finding solutions to problems, etc. Now that it's been designed, built, and tested a few times I figured I should post here.
I'm going to break this down into parts/chapters to make it easier to digest or if you just want to skip to the bottom to see videos of fruits exploding.
Chapter 1: The Idea
After making a very underwhelming metered propane cannon that only worked about ~50% of the time (very nerve-wracking btw), I decided to look for better options. I quickly found this place, and after taking one look at the hybrid section, I decided to build a pneumatic cannon.
I’ve always loved tanks and tank combat, so I decided to attempt to make it look like an anti-tank gun, meaning I’d also need to make a mount of some sort.
Therefore, I set some main objectives for this build:
- The barrel will be at least as tall as me, and 2” in diameter
- It will be fully breech-loading, no disconnecting barrels or other nonsense
- It should be able to easily be placed into a mount for the cannon that can elevate, traverse, and is easily transported (at the time, my biggest car was a two-door VW GTi so space was at a premium)
- It will be bigger and more powerful than my last design (not hard)
Chapter 2: The Valve
Despite not being 100% confident in my understanding of them, but being somewhat confident in my ability to build one, I decided to build a chamber sealing piston valve. Taking elements of the supah valve, designs from multiple other websites, and numerous threads here, I came up with my first design.
Nothing too special here, just a piston made out of a bolt, washers, plywood, etc.
However, as I started finding the materials to make this, I started to have doubts about the integrity of it and if it would seal. Again, I didn’t really understand this, like where the air goes, how it gets to the chamber, etc, so I went back to the drawing board.
Here's what I came up with:
Having discovered solid PVC rods on McMaster and coming up with the above design, I got a friend with a lathe to turn the grooves for the o-rings and drill the hole in the center for the check valve. Feeling good about my design, I spent the next 3 days building, fitting, and buying parts. Finally, it was finished.
I started to fill it with my tire inflator (didn’t have a compressor, I was gonna shoot this at my friend's place anyway), and oh boy did it leak. It really leaked.
I spent the next week working dusk till dawn sweating my ass off in my garage trying to get it to work before I left for a cross-country trip so I could have some closure. Alas, the highest it would hold was 30psi.
Then, while looking through threads on this forum somewhere in Montana, I found a thread where someone was talking about industrial dust collector valves. Did some digging, found a site that sold them, and ordered a 2” Goyen Pulse Valve. Two days after returning from the trip, the cannon was complete.
Chapter 3: The Mount
Having already spent so much time on this project, I simplified my ideas for a mount, deciding not to bother with the traverse mechanism. After spending a couple of days building and troubleshooting, here's what I came up with:
The cannon itself is clamped to the mount by the two wide vertical planks at the front and back of the mount. The rear legs can be removed to save space, and the elevation mechanism is a long threaded rod run through a nut near the chamber.
Chapter 4: The Ammunition
Remember how I said I like tanks and tank combat? Well, admittedly this thing wasn't designed to shoot potatoes. Rather, it's primary ammunition would be these:
Heavily inspired by modern APFSDS rounds, I found 12” long nails and crudely affixed sheet metal fins to the rear using a piece of PVC and epoxy. I used that pink solid foam insulation to make a sabot for them and also for wadding behind it.
Along with these, the main things I shot were potatoes, tangerines, sections of 2” wooden dowel, and handfuls of small rocks wrapped in a paper towel.
Chapter 5: Testing & Function
My biggest success of this whole thing was the breech-loading. I used a modified reducer bushing to pass the barrel most of the way through a larger Tee with a female adapter and a threaded plug on the back. Here’s a video demonstrating it:
Having shot it once in my garage and swiftly coming to the conclusion that shooting this thing in the city was a bad idea, I packed it all up and set off to my friend's house.
One of the big things I was interested in with this project was how effective the dart rounds I made were, so I’ve compiled some of the footage from those in the video below.
Finally, here is the exploding fruit I promised, along with a few other things.
Thanks for reading!