This is my fully welded stainless steel spudzooka, its simply 2 pieces of stainless pipe, 1.5 foot 4.5" diameter combustion chamber to reducer to 3 foot 2" Barrel. The cap on the end in a giant hex nut with a stainless plate welded in. The switch is powered by a single AA battery and is wired up to the spark from a superser portable gas heater.
To load its simply a matter of placing a potato etc. over the muzzle and pressing a snug piece into the barrel before using a plunger to push it til it meets the reducer. To prime it i use hairspray, 3 squirts is the perfect amount! To fire you hit the switch and Boom
I might upload a vid of this onto my youtube channel if i get a chance!! It shoots more than 100m easy and can shoot a frozen potato through 12mm plywood at 10m. Good fun....