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Building Your Own Airgun

Preparation
Now that you have everything, where do you start? Begin by cleaning the steel pipe inside and out with a solvent to remove all traces of grease. You especially dont want grease on the inside as high pressure air and grease can spontaneously ignite. After cleaning, coat the male threads of all pipe and fittings with teflon pipe thread tape. This will create a seal and prevent the air from leaking.

Cut your 1/2" copper pipe used for the barrel to your desired length. I have found that 16" to 32" is ideal for most applications. Remove all burr and sand the breech end of the barrel until it is bright and shiny. Brighten up all the fittings at this time as well with the sand paper.

The Hard Part, Making the Action
Take a plug fitting and clamp it upside down in your drill press vice. Drill and tap a hole to 1/8" NPT. Apply thread tape to the 1/8" end of your Schrader valve and thread it into the outside of the plug fitting.

Thread the plug into a coupler and thread a pipe into the other end. This will be your air reservior assembly. The length and diameter of the pipe is important here. I have found that a 18" length of 3/4" pipe works really well. Since we will be filling with relatively low pressure (300 psi as opposed to 3000 psi), a large volume of air is necessary to get good velocity.

Thread a 3/4" to 1/2" reducer fitting to the end of the pipe. Take a 2" length of 1/2" pipe nipple and thread it into the reducer fitting. Thread a 1/2" ball valve onto the other side of the pipe nipple. This will be your firing valve.

We are almost done with the action of our homemade airgun. We now need a way to attach it to the barrel assembly. Set the action aside as we change gears a little.

The Hard Part, Making the Barrel Assembly
Silver solder a right angle copper fitting onto the end of a copper pipe to 1/2" npt adaptor. Cut a 1 1/2" length of copper pipe and brighten it up with sandpaper. Solder that to the other end of the right angle fitting. Solder a T-fitting onto the other end of the piece of copper pipe. Solder a copper pipe to 1/2" NPT adaptor to the right hand side of the T-fitting and put a 1/2" pipe plug on. Dont tighten this plug too much, as that is the loading port. On the left side of the T-fitting, solder the barrel.

Putting it all together
You can now attach the barrel assembly to the action. Double check that all connections are securely tightened. Failure to do so will ensure slow leaks. We all know what that means... Here is what your airgun should look like at this stage:

Testing Our Handiwork
This is perhaps the most dangerous part. I recommend that you place the gun under several layers of blankets in the event of pipe failure. Fill it up to 40 psi and check the gun for leaks. You can spray each connection with soapy water to assist in leak detection. Any leak will blow small bubbles. Tighten any leaking connections and recheck until all leaks have been stopped.

Discharge the airgun by pointing it in a safe direction and opening the ball valve. You should hear the air escape the barrel. It is surprisingly quiet. Go ahead and fill the gun to 125 psi, the max pressure of most air compressors. Check again for leaks. If there are no leaks, you can permanently seal the gun with epoxy or Quick Steel.

That wasnt too bad, was it? You have just built your own airgun capable of producing muzzle energies in excess of 50 foot-pounds. Now it is time to load our gun up and take some practice shots.