I've heard about them. I would like to build one. Can't seem to find out much more though.

1) Direct yourself to your nearest search engine

2)type in "potato gun"

3) press search, or go or the sorts

4)build your potato gun

my cousins built one kinda like a pipe bomb it was really cool they had it working but then they stopped using it for a long time and then when they whent to use it again it wouldn't work.

Yeah, mate
I built one with a fat piece of drainpipe, about 10 inches in diameter, and about 3 foot long, with an endpiece which was made to fit it on one end. On the other you need to find some way to get a 4 inch bit of pipe, about 5 foot long, to fit. You can get downsizing adaptors, but I used shit loads of duct tape instead, but you need to make it secure, and need some chicken wire taped around the 4 inch dia barrel to stop your ammo falling into the combustion chamber.
In the way of power, I used butane gas, but any old explosive gas should do the trick.
You need to drill a hole in the side of your 10 inch pipe to stick a pipe into for pumping the gas in, and when you stick the pipe in you need to make sure that is well secure too, otherwise it will blow out and take your eye out.
For ignition i suggest an electric system such as a barbecue lighter, shoved in a hole in thew side of your 10 inch pipe, or rigged in after taking it to peces, as I did, with the clicky bit attatched to a 6 foot piece of wire (I was a bit apprehensive about the first shot), and then simply click the clicky bit and it should fire. You neednt go for a long wire though, as it is perfectly safe...
The end product will be pretty large but very powerful and incredibly accurate.
just get it held up by something and let rip.
when it comes to firing just pump in the gas for about 10-to-whatever you please seconds, click your clicky thing and you should fire your load nicely.
Mine will fire potatoes about 150 yards, and tennis balls about 300-400, but with a little effort you could build one to better that.
+ be imaginative with the ammo. should provide endless hours of good clean fun.........

go to the nearest hardware store and purchase the following items:
1)2 ft of 1.5 inch pvc pipe
2)1 ft of 3 inch pvc pipe
3)a 3 inch to 1.5 inch reducer
4)a 3 inch fitting thats smooth on one side and goes to threaded on the other
5)a 3 inch cleanout plug
6) a bbq grill ignitor

put them all together

if u dont get it u can always look for directions on a search engine

I tried building one but it sucked ass and Im gonna try again. I found our main problem was we were putting to much fuel in tthe chamber and that wwas only with a few seconds spray of starter fluid. Go for a quick burst and try that yah gotta mess around a bit. I also found grill igniters while commonly suggested SUCK. but if yah gotta use em soder on a paper clip so you can get a bigger spark and the fuel dosent gum up on the igniter. I found a nice flint igniter to work well. Like a coleman latern lighting thing or I got this sweet minerature cannon igniter that you slam down and sparks fly.

OOOHHHH ITS SO DAMN HARD, (YEAH RIGHT)Make your own design, u could do anything almost to make one, u need no stupidass exact design or anything!

But if you're a lamo, then you can use xinventions.com

Kinda good