The chamber is a Nalgene 250ml polycarbonate jar (bought at http://www.usplastic.com). The barrel is a 6.03mm tightbore airsoft barrel with a length of 300mm. The barrel is supported inside the chamber using two 2" diameter acrylic discs (also bought at usplastic) and a TON of epoxy. One of the things I wanted to incorporate to this cannon is the rubber washer on the barrel at the breech. Not only does it hold the bb stcurely in place, it also grips the bb tightly, and only releases it once pressure builds inside the chamber (like a burst disk). The rubber washer increases performance significantly. Ignition is a normal piezo sparker housed inside 1/2" pipe and fittings. The spark "stick" has two spark gaps and is made out of a bic pen, 18guage copper wire, and epoxy (slightly ghetto). The fill valve on the front of the chamber was salvaged from a airsoft gas blowback gun magazine. it just so happens that the nozzle on butane cans fits the fill valve perfectly, so I epoxied the nozzle of a butane can to the end of a 12ml syringe for fueling (see video).
And the video:
In the video Im shooting a .20g bb through both sides of an aluminum can, through the cardboard backstop, and the bb proceeded to fly across my appartment seeming un-phased by the can and box.
