Damn dude.... a couple years ago that was all i did. Mod those nerf guns into airsoft and go wild. I gotta look for the link, but I used to use a pretty simple system that worked great. Yes it was semi-auto. Anyways.... man the memories.. ill find that link for ya.

I am in the process of finishing my primary pneumatic rifle. Underneath the gun i have an ideal place to put a short shotgun. All I plan to to is use a simple ball valve setup with 3/4" pvc as the tank, 1/2" as the barrel and load with shot. My main rifle uses a piston valve and I love it.. but its ...