No pics - just fond memories.

Making one of these things isn't brain surgery. The sizes that Dogfish said are about right. Don't go super big = danger.

My biggest reccomendation is be very, very careful. Use common sense (common sense would probably tell you not to make one!). Do not under any circumastances use black powder. This is a very, very bad idea.

Here is a collection of ideas I have about the guns to make them work better and make them a little safer. For a charge use something like hair spray. Starting fluid might be a little too volatile and flammable and can give you a head ache (ether). Use no larger than 4" for the chamber - use a section about 1-2' long. Drill a small hole in the chamber and install a latern flint as an ignitor, they work pretty well. At the end of the chamber use a srew cap. Use a small amount of propelant , usually a spray about 1/4 of a second long is all it takes. Too much and you will flood the chamber by making the mixture too rich. A 4" chamber approx 1-2' long has a relatively small volume that will not generate huge amounts of pressure (this is a kind os built in safety feature). Sharpen the end of the barrel so it will cut the potato to the right fit. Use a broom stick to push ammo down barrel.

Above everything else is be careful. I'm sure poking around the internet can yield some btried and true plans. Please use cation when playing with these things.

Alright have I said be careful enough? Can you see the dad in me come out? Have fun - be safe.

Steve