In this Instructable, you will learn how to build an air gun from just a fire extinguisher and a few other small parts. The spring and o-ring inside the fire extinguisher valve will outlast the Air Coupler.
DISCLAIMER: I AM NOT RESPONSIBLE FOR ANY INJURIES OR DEATHS RESULTING FROM BUILDING OR USING THIS DEVICE. ALL RISKS ARE YOURS. PROCEED AT YOUR OWN RISK.
Update: The valve started leaking, so I machined an adapter to fit in the tank so I can use a QEV, ball valve or whatever to fire.
Step 1: Tools and Parts
1/4 inch NPT die
Light machine oil
12 volt car air compressor
1/4 inch female NPT air coupler
Two 1/4 inch NPT female air plugs
1/4 by 12 inch NPT nipple
1/4 inch by 1/8 inch bell reducer
1/4 inch by 25 foot coil air hose
Step 2: Extinguisher Prep
Discharge the fire extinguisher anywhere you like. Then, remove the valve from the tank. Dump out the remaining powder. Remove the nozzle from the valve.
Step 3: Tapping
Clamp the Nozzle in the vise, threaded side down. Using light machine oil for lubrication, tap the plain end with the die.
Step 4: Air Hose and Barrel.
Connect the female air plug to one end of the air hose. The bell reducer goes on the other end, and on the remaining end of the reducer, connect the tank valve. Connect the other female air coupler to the nipple to make the barrel.
Step 5: Shooting
Hook up a car air compressor to the tank valve, hold down the trigger on the fire extingisher and pump to 20-200 psi. You can shoot foil balls, BBs wrapped in foil, or .22 ammunition with a ball of wet toilet paper behind it. Steel balls are also a good choice.