Well, it seems like now-a-days if you need a part for a gun...or a whole gun itself, you can just buy a 3-D printer and print off whatever you want! I could see this being pretty useful for airsoft, but I'm not so sure I'd want a live explosion in that thing.
http://motherboard.vice.com/blog/the-3d-printed-gun-store-is-open-for-business
Wiki Weapon - 3D Printable Gun - Defense Distributed
http://motherboard.vice.com/blog/the-3d-printed-gun-store-is-open-for-business
Wiki Weapon - 3D Printable Gun - Defense Distributed