Ah-ha. I have an old gas grill igniter laying around my garage somewhere. Looks like it's going to be an interesting weekend. Thanks!
You have to be careful. The ignitor fittings need to be tapped to the correct thread size. Also, some kind of adhesive needs to be used on the threads. Don't forget that PVC needs purple primer and PVC adhesive. Otherwise, your 'tater gun just spits stuff out the back end. *AND* my potato cannon does launch with enough force to be dangerous. You need wide open spaces(the Outer Banks was perfect). I used a broom handle for a ramrod. Sharpen the edge of the muzzle, then you can use oversize spuds. I got 150 yards with just a few spritzes of Auqanet hairspray...