Has anybody made a potato cannon here?
i have made 2 they are combustion driven. you spray starting fluid in the end and light it with a grill ignitor and it shoots over 500 feet 
mmmm no comment.
it might not have been potatoes
tennis balls maybe?
I have also made two. One large and another smaller, hand held one. Both fueled by butane or propane. I have never mesured mine but imagine my large one goes around what yours does and my smaller one goes around 100m. They destroy most things you shoot them at. Good fun to play with and eveyone who comes around seems to be amazed by them. I made a quick video of my large one and put it on youtube. I have filmed some shots of my small one but havnt edited them together yet.
I would be intrested in seeing some photos of your designs maybe.
I am yet to find a barrel that a tennis or golf ball will fit down snugly 
Here is a quick shot of my small gun from the video I am making of it…
spud gun.bmp (1010 KB)
My brother and I had (have) a potato cannon. One time we ran out of my mom’s potatos from the kitchen, so we shot dog poop out of it.
my older bro. made a potato cannon and wedged a tennis ball in it so it was really tight
boom
Thats pretty nasty. I once put a dead rat down the barrel and shot that though 
We fast ran out of potatoes and since we have loads of apples on our trees I normaly shoot those. Sweet potatoes work well if you can get them down the barrel, they are really hard and do alot of dammage. Onions dont work very well because they start to peel them selves in the air and they sting your eyes if you shoot things close.
Anyway, lets see some of your guns/cannons…
I can’t even count how many I’ve made.
Even made a two-stager once. That was wild.
I found Propane to be the easiest propellant to use, as I could just put a fitting on the back of the gun, near the grill igniter. I got way more than 500 foot range. You also don’t get on some FBI watch list for buying 6 cases of ether starting fluid 
Re: tennis balls: a soda can fits a tennis ball very snugly. Three cans taped together, little white gas, match hole in the bottom: could lead toa a hell of a weekend.
2 1/2 inch PVC works great for tennis balls. It’s a little hard to find that size pipe but they do make it.
I will look out for some thanks. Do you burn the hair off the tennis balls or leave them as the are? A barral that would take golf balls would be awesome too. found anything that fit them?
You can use the tennis balls just the way they are. I once heard that there is a type of PVC pipe that fits a golf ball, but I have not tried that yet.
I always use hairspray as fuel, because it’s already aerosolized and it’s cheap to obtain, and I use a grill sparker to ignite it. I don’t have a picture because I’m at college right now, but it looks alot like this:
If you have something too small for the barrel, use a sabot to shoot it (basically wrap it in something until it fits the barrel tightly). My barrel fits a small paper dixie cup just about perfectly, so I usually use those to propel anything from golf balls to paintballs. Paintballs work really well :~) It’s a giant paint shotgun heh heh
we use socks wrapped in duct tape for ammo when we dont have potatoes!
I had a combustion type and a compressed air one. Compressed air is definately the way to go. Much farther distances, works every time, much more controlled.
sp4rky that metal cannon is awesome is that brake lever the ignitor? i would post my gun but my computer takes to long so here is a link of the plans i followed. http://dangerouslyfun.com/spud%20gun , i made 2 but one of them has a shorter combustion chamber and the other a larger one. i can never get a snug fit with my potatoes so i just use apples off of our trees. one time i was bored so i shot an apple at this small shed at my house about 200ft away and it went completely straight and right through the window and almost made a hole in the wood on the other side!
i think i might make like a 10ft long compressed air gun. it gets annoying after a while of your gas not igniting.