We have covered a bunch of cool BB guns here in the past. If you are looking to take your game to the next level, you may want to build your own BB machine gun. NightHawkInLight has accomplished just that. His BB Machine Gun can fire over 5000 rounds per minute.
As you can see in the above video, this machine gun has simple parts. The trigger is an air compressor blow gun while the hopper is a small soda bottle. You can find out more about it here.