I've been working on a semi-automatic pneumatic version. Current setup uses a MJVO-3, clippard cylinder, and hornet tank. I slapped this together in a few hours from scraps so excuse the horrible machining. Trigger has not been setup yet. It's currently 10" long, 6.5" high, and 1.25" wide. Currently running it off a magstrike bladder. Not all that practical for a war but a fun project to work on.
Not pictured is a rubber band that returns the slide and all the tubing. The weird contraption on top of the slide is my take on a delayed blowback system. Without it the breech will open before the dart has left the barrel. Currently suffering from low airflow from hornet tank due to the sharp bend it undergoes before it entering the barrel. Any suggestions?
Edit: Can't seem to imbed a photo, sorry about the link!