Making a potato gun is practically a right of passage for some kids. It can however be very dangerous and caution must be taken during construction to build a relatively safe potato gun.
Purchase thick-walled plastic pipe and fittings from your local hardware store in the following dimensions: 2 feet of 3 inch pipe, 4 feet of 1 1/2 inch pipe, a 3 inch to 1 1/2 inch reducer fitting and a 3 inch plastic pipe end cap that unscrews.
Remove a grill igniter from an old grill.
Use pipe glue and assemble the end cap onto one end of the 3 inch pipe, and the reducer on the other end. Let dry.
Connect and glue the 1 1/2 inch pipe to the reducer.
Drill two screws into the back of the 3 inch pipe about 3 inches from the end cap. Position the screws so that they come from both sides of the potato gun chamber and are about 1/2 inch apart inside the chamber.
Attach the 16 gauge wires to the grill igniter wires on one end and one to each screw on the other end. Now try looking inside the gun and making sure when you click the igniter you get a big spark between the screws. If not, reposition them.
Cut a potato to fit tightly into the barrel and insert it all the way down the barrel. Spray hairspray into the larger chamber, screw the lid tightly shut and click the igniter and watch the potato fly!