A way to send halloween treats into the sky, without wadding or dangerous projectiles.video
see the video. 3 sec. hang timefor the candy. container didn't leave the barrel because of loose seal.
Step 1: First you need a large barrel potato gun.
This is the threaded end, where the fuel goes (I use ether). I added screws in addition to the ABS glue for extra strength, although it probably isn't necessary. It is also your access to the ignitor (see next step) and how you ventilate the cannon between shots, to get some fresh air inside quickly.
Step 2: The ignitor.
I put mine about 8 inches from the end cap. Close enough to work on. It is a replacement barbeque ignitor that comes with a AAA battery powered ignition switch. I sealed the holes with silicone. You can bend the wire electrode until you get the gap that's right for you. On the outside, I reinforced and protected the connections with epoxy, since they are a little fragile for this application.
Step 3: The firing button.
If you are unfamiliar with barbeque ignitors, the battery is underneath the red button. I put mine too far along the barrel to use fasteners which might protrude into the barrel. So it's two-part epoxy and lots of black tape. I stretched out the supplied wires as far as they would go.
Step 4: The most important part.
Once you have built a 4 inch barrel potato gun, you will probably realize that pototoes are too small to touch the sides and you can't build any compression. Rutabegas work, but firing off 2 dozen of those gets expensive. Wads of wet newspaper is labor-intensive and messy. Bigger suddenly isn't better. However, if you take a yogurt or cottage cheese container, and trace around it snugly in the barrel, you get a perfect fit.
When you are done, cut off the excess, and see if it fits tightly.
Now, for a little strength and better compression, wrap the surface that will contact the barrel with some electrical tape.