Years ago belonged to the NMLRA, and subscribed to their magazine, Muzzle Blasts. I am pretty sure it was in one of those issues that I read about a working model of a Gatling Gun that the guy had made, steel cylinders and all. I don't recall the caliber, but do recall he said it took awhile to reload all those cylinders so he could shoot again. I have not a clue what issue it would be, but I'm sure it would be possible to find out. I don't recall if there where any pictures of the innards or not.
I've got a set of the RG-G plans, I understand that one is better for shooting; the other is prettier, but supposedly not quite as reliable. I'm gathering materials and .22LR ammo. Hopefully one day.