If you've got a spare weekend and have the tools laying around, then why not build your own 25MM Pneumatic Sniper Cannon? Well, that's exactly what this group of friends did. Video after the break. Click here for more pictures.
Boasting a two-and-a-half-foot barrel that is one inch in diameter, the rifle has custom bolt-action mechanism, a modded sprinkler valve as the primary firing valve, and a $40 sniper scope[via Gizmodo]