Youtube user TopCityGear had experimented with a nerf blowgun before, but decided he wanted a bit more capability. The result is an air-powered gun made from PVC, a gutted cordless drill, and a sprinkler valve.
The air reservoir is pumped to capacity with a standard Schraeder valve. The air then passes through the empty cordless drill and into the sprinkler valve. The man behind TopCityGear came up with an interesting hack here. He wired the trigger of the drill to the actuator in the sprinkler valve, giving him realistic control over his shot.
The video gives pretty detailed explanation of the device, but if you want to skip to the action go to 8:25.
[via Hacked Gadgets]