Anyway, it made me start thinking about building a cannon that operated like an engine. (igniting a mixture of fuel and air with an electric charge and using the energy released to drive a projectile rather than a piston).
So I went to Home Depot and started buying a bunch of piping, fittings, cements, sealants, and a piezoelectric igniter.
Built two guns, I have a video of me using one of them.
Click here for video of small spud gun.

Daiwa sticker


Used RTV and screwed the igniter into a 5/8" hole in the tee joint. That's 1.5" barrel and 3" chamber.

Igniter leads run inside the chamber and come through a small hole where they are attached to 2 large bolts that create the spark in the chamber.
They are attached to the bolts with hex screws.


That wire in between allows me to adjust the gap.
NOW FOR CANNON #2 THE WHOPPER!!!

That's 4" chamber and 1.5" barrel.

I made the igniters removable by bolting them on and then sealing them with rtv.

The spark jumps to one of 8 prongs on part of what was the gas concentrating vortex that came with the igniter, it is suspended by a small cable from an old dremel snake.

Notice the stopper in the barrel, that is present in both my guns.

Nitro cleaner is pure methyl alcohol, my favorite fuel.

This target was shot from about 60 feet away with the whopper, this picture shows the back side of it, it's a half inch of plywood.

a couple shots hit the wheel barrow

Those are my cannons
-Matt