Kallahar built a complete autonomous gun platform called the the Robot Airsoft. He documented the whole thing, providing a complete parts list, software, and even the autocad files. He does everything but build it. Still too lazy? He will build it for you and test it.

He said the design would work well at the Defcon Robot Contest or at the RoboGames event. He should know because he is the organizer of the Defcon event (and thus unable to compete). He competed at Robogames and took second place. <via Hacked Gadgets>

I have seen many coil gun build ups. The nice thing about this one is that you can build it pretty quickly with almost no money. All that you need is used disposable camera with flash. Add a few parts and there you go! Want a magazine and laser site? Jeff did that. Here is another one that is more serious.