It looked to me that this would have external power, and the three turrets rotated by a chain... So what exactly is the proper nomenclature for the gun I posted?
The multiple rotory barrels in your photo are also driven by an electric motor, however, the entire reciever, bolt and barrel turn, with the bolt, guided by a track, moving back and forth.
The Apache attack helicopter has, or had, a single barrel chain gun under the nose, aimed by a device attached to the pilot's helmet.