What Did I Make?
I am 16 years old and made a covert air powered bb gun, that is rapidly realizes a burst of air to propel a projectile at maximum possible velocity. I wanted something powerful, yet small and covert, so I chose a maglite flashlight because it could hold high pressures, and had a threaded back cap, which was crucial to a serviceable design
How did you make it?
This was made by first disassembling the flashlight, and gutting the bulb assembly, then you are left with a empty tube. The barrel is then centered and epoxied in so that there is room left at the bottom for a piston to move. The battery cap to the flashlight is drilled, and fitted for the Shrader Valve, and then is epoxied in. Finally a piston is fabricated by stamping a thick piece of rubber. The whole thing is assembled, and is pressurized with the pump, the gun is fired by pushing the pin in the shrader valve. When the valve is pushed, a small amount of air is vented, causing a suction to pull the piston back and dump the rest of the air into the barrel.
Where did you Make it?
I made this at my home, and in my garage. This was a fun summer project for me, and it turned out very nicely.
What did you learn?
I learned the basic principles of Penumatic Design, and methods of achieving supersonic velocities by using physics equations, and simulations. Using the equations for drag, and velocity I was able to estimated the pressure with about 9% error to the actual thing, which was measured by a chronograph to 850 feet per second.
High Pressure Epoxy (JB Weld should work)
Pipe cutter (or metal saw)
Mini Mag lite
4.5mm internal diameter brass tube (varying length, check next step)
Shrader valve (from bike tire)
Shock Pump (sold at sporting stores)
**if you need more help go to www.spudfiles.com**
Step 1: Barrel Assembly
100psi- 8 inches- 600 Feet per second
200psi-12 inches (suggested, easy to pump to pressure, and almost supersonic velocities (850 feet per second)
300psi-24 inches- 1000 Feet per second
The barrel I recommend is a 4.5 mm internal diameter brass tube, because this will leave you with substantial air flow, and ammo can be bought as steel bb's from the store. A centering jig for the barrel can be achieved by wrapping a bamboo skewer in tape, so that it is centered with the main body of the gun.
Step 2: Piston
* A piston can also be made from plastic, with a rubber sealing face, and then wrapped in tape till it fits*
Step 3: Valve Assembly
Step 4: Final Steps and Shooting
Step 5: Troubleshooting
The piston is too tight, and it must be shaved down, remove it and use trial and error to make it perfect
Gun vents all air when valve is pushed?
The piston is too loose, and it must be remade or wrapped in tape.
There are leaks but I cant find them?
For a small launcher like this, leaks can be hard to find. To find them, pressurize the gun and put in in water, find the bubbles and epoxy it
Threads are leaking?
The pumbing tape must be tight, and pliers may be needed to attach the valve cap.
Spudfiles.com (Specifically Mr.Crowly and Jacksmirkingrevenge)