How-to website Instructables is running Launch It, a contest for people to send in their homemade inventions. And here's one of the entries, a 25mm pneumatic cannon. 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 on the top. I love the fact that one minute the brains behind the weapon is reminding us about safety goggles, the next he's telling us that PVC is undetectable by X-ray machines. [Instructables]