Step 1: Materials
-2 Soda bottles. I used coca-cola but as long as the bottle necks are the same it's ok.
-2 Lids to fit the soda bottles with the blue seal intact.
-A short length of pressure PVC pipe. This holds a large amount of pressure and fits very tightly with a friction fit inside of a bottle neck.
-A preferably non-brittle pen.
-Piezo electric sparker. Can be found in some lighters, BBQ lighters etc. Just need the kind with the brass contact and a single thin wire.
-Flexible PVC/plumbers' tape.
-Hot glue/hot melt gun and cartridges/glue sticks.
-A drill or a very sharp knife, but the drill is highly reccomended.
-Exacto/hobby knife. Any sharp knife will do.
-Sandpaper/emery paper or a smooth file.
-Hacksaw, preferably with a fresh blade.
-Propellant: Deoderant/cologne, butane, propane, hair spray etc. Do not use fuels such as petrol, LPG, diesel or higher combustion gasses such as hydrogen.
-Ammunition: Spit wads, potato pieces, Q-Tips, whatever you use.
-Acetone and a rag to apply it with. Be very careful with this. The fumes are terrible and try not to get it on your skin (though it removes a lot of glues).
Step 2: Preparation
-Cut a 3cm length of the PVC pipe which fits snugly into the bottlenecks. Remove the burrs and sand the ends smooth. If you have acetone, apply a small amount to a rag and use it to clean the outside of the PVC.
-Drill a hole in one of the bottle lids large enough to tightly fit your pen barrel. In the other drill a hole that will tightly fit the brass terminal and a small hole to fit the wire.
-Remove the contents of your pen (spring, ink etc.) and discard. Use the hacksaw to cut to the desired length. Trim with an exacto knife or sandpaper.
Step 3: Assembly
Push the barrel a short way into the larger hole, and the glue on both sides with hot melt glue.
Place the brass terminal of the piezo into the other cap, then bend the wire down into the smaller hole. Position them so when you click the button a spark jumps from the wire to the terminal. After that is working hot glue it in place.
Screw the bottle caps onto the neck and the gun is complete!