Although it may not be the first ever made, it certainly is one of the best to date. I would classify this as a prototype, it is far from perfect but it DOES work. Unfortunately I was only able to use it for a few days of the fall 2010 SBU HvZ game as it was damaged when a zombie caught one of the hoses and cracked the shell. It is of course fixable I just would rather make a new more improved version (Flywheels.... that's the only teaser you're going to get ;).
This Instructable will hopefully be viewed by a few other forums as I hardly have the time to even write this.
DISCLAIMER: Modifying a NERF gun in this manner will permanently alter it. This instructable should only be used as a reference, as your specific modification will be different. NEVER use a CO2 canister that has not been properly filled. This modification should only be attempted if the proper tools and safety precautions are employed.
Why do we go all out for HvZ? Because when else are we going to be able to deck out in tactical gear and run around campus with NERF guns?..... THAT's why =)
A sample of the magnificence: