Question:
I love spud guns. But I could never get them to work properly. Getting the mixture right and keeping out the damp always seemed a difficult task. I never managed to make a gun which would fire reliably. But this week I saw a local place selling off 5 kg carbon dioxide fire extinguishers cheap. And I wondered if perhaps I could use one for a spud gun. I guess the critical factor is whether or not the carbon dioxide can exit the cylinder quickly enough. But even if it can't, one could make a gun with a smaller barrel I guess. Anyone tried this? Is it a workable idea? Any idea how many shots you'd get from 5 kg of carbon dioxide? It should be possible to work it out, but after a few moments thought I can't see how.

Answer: -I have not tried shooting bits of potato, but did make a similar gun that fires a 1 inch diameter steel slug that weighs about a pound. The slug has a nylon cord attached to it and I can shoot it over branches high in a tree. Then pull a steel cable up and around the tree, so I can make sure the tree falls where it will do the least damage. Do be careful. While perfecting this, I lost several slugs and worried that they may have landed in the neighbors yard about 500 feet away. And that was with the gun pointed nearly vertical.

-Oughta work, . Air rifles have been using carbon dioxide for years. Likely your problem will be "metering" the charge into the spud gun. Fabricate some sort of a hammer falling against a valve to meter a charge. Air rifles used to use something call "Hycar" as I recall. Think "O" rings, maybe.