| I have built two, a 1-1/4x2 and a 2x4. Each is about four feet long.
The design I followed can be found at the
Backyard Ballistics pneumatic gun page.|
I wrap the chambers of the guns in a bath towel when firing for safety, a couple long nylon hose ties hold the towel in place.
| I believe I have found the perfect diaphragm material, it is 3/16 hard neoprene
with cloth insert. I got it at a manufacturing company I worked for, I don't know where
to get it locally. It is advertised in McMaster-Carr supply (708)833-0300 catalog if you
have access to this catalog as "cloth inserted neoprene sheeting" with a tensile strength
of 1000 psi. I have used this in both of my guns and have not seen any deformation with
pressures reaching 120 psi.|
I will mail, at my expense, a 5x5 swatch of this material to the first dozen or so to e-mail me concerning this material. You must include a waiver of responsibility statement that I would accept.
| The air supply I use for my guns is a water (empty) fire extinguisher, I pressurize
this with a small compressor to about 120 psi. It is rated for 200 psi and has a gauge
at the valve, I fitted it with an air hose and a blow-gun. I can get about 10 shots
with my smaller gun and only about 3 shots with my 2x4 gun. My next upgrade is to rig
a small well-water tank, they are usually rated at 150 psi and I should get many more
shots out of it.|
The wrench in the picture was fashioned out of top-rail (fencing) tubing to fit the 4" cleanout plug, so I don't have to carry my tools around with the gun.
| My first attempt was to mash an aluminum can for my 1-1/4 gun. I reduced the
diameter and placed it into a short pipe, then mashed it down with a ram rod of a
wooden dowel. The can mashed easily, but the projectile was lame as there is to much
air spaces within it. Maybe a wad of cloth would aid the load.|
|My current attempt is to melt a quart motor oil bottle (empty) in a short iron pipe nipple. I cut the bottom out of the bottle, placing the bottom into the bottle, then slit each narrow shoulder of the neck. Next I flatten the bottle and fold lengthwise, and roll into a tight cylinder. Force this into the iron nipple, place into the oven or heat gently with a torch. The soft (hot) plastic can be formed into a point to aid in accuracy. This cools into a VERY hard projectile, caution is to be emphasized, I only shoot this straight up for hang-time. I have created one of these and they work very well.|