The pneumatic pen gun using a coaxial piston valve is fairly well known, while the exhaust valve design is nothing new I lay claim to having made the progenitor back in 2007 for a spudfiles.com forum contest as featured here.

The method of filling and firing is shown in this simple animation.

Since my first effort I have gained access to machine tools and have made several much improved versions. Here I will show the steps in the manufacture of a pen gun with a carbon fiber body.

Step 1: Main body

The main body is cut from a length of 12mm OD - 10mm ID carbon fiber tubing roughly with a fine toothed hacksaw, and the ends are then squared off and cleaned up on a lathe. In order to protect the finish, masking tape is wrapped around the tube before placing it in the lathe chuck.

<p>This is very cool, but I am not clear on the details of the trigger valve and how it interacts with the Schrader valve and the charging/firing cycle. Can you please add more details in these critical areas? I would think a simple schematic drawing depicting the &quot;air circuit&quot; showing where the pressure is stored and how it is released, as well as a cutaway drawing of the Delrin piston components - unassembled, please! I'm sure you have different implementations with your varied models, does this carbon-fiber model represent the pinnacle of your development? I would like to know more about your insights gained in the learning process ... and see more of your work of course!</p>