This site contains instructions for building your own semi-automatic air-cannon designed to fire rolls of toilet paper.
This will be handy if we’re invaded by the kind of Klingons that hang around Uranus.
The real ingenuity lies within the auto loading mechanism of the cannon. It uses a bolt-like system which grabs and places the ammo in the barrel, directing the air flow only to the projectile being fired, and springs back to catch another projectile automatically. This in turns enables this cannon to be a semi-automatic cannon. As said earlier this loader can be used to design a full-auto air cannon relatively easily. Xinventions, is in the process of designing this full-auto cannon, and more info will be available to the public soon.
(via Red Ferret)