Here is a full-scale Sentry Turret from the game Portal that can open/close, move its weapons, and activate a laser from its eye. It has a camera to track targets and uses 4 Nerf guns to shoot at targets. As ytec3d explains, it took 300 hours of 3D printing to make this.
The turret can open/close automatically. It can move 20 degrees in all directions. The turret is controlled using an Arduino MEGA.