thanks guys! i really appreciate the help. i reduced the gap to about two mm and i tried a different kind of hairspray at the suggestion of a friend and i'm all set now. Aqua Net. in a purple can w/a white top. my gun is made from a 3" y connector with two cleanout caps attached and a 3' long barrel...

just finished up making a basic launcher and i've only launched about 4 spuds so far. i'm using a replacement grill igniter and hairspray for propellant. if i dont have a potato in the barrel and i spray in a 2 second shot of spray,stick the cap back on and hit the igniter it'll go off. do the same ...