High-Power Pneumatic PenGun

Hey guys, this is my first instructable so please bear with me. I recently made this video about making a pneumatic pen gun. Please enjoy a let me know what you think. :)

NOTE: This is a piston valve, coaxial pneumatic PenGun. If you want to attempt this project, make sure you're dedicated and completely understand the concept of operation. (The concept is explained in the video) For those of you who don't know what I just wrote, this aint powered by no rubber-bands :D

WARNING: This thing may be small but can pack a serious punch at high pressure. ALWAYS wear safety glasses when operating and NEVER point at any living thing. Don't shoot your eye out kid...