No; that's not a Manowar song (although it sounds like one

).
Yesterday I received a squad of 2nd edition metal Nurgle Space Marines; quite chuffed with them. But in the lot (unbeknownst to me) were included two (identical) metal Chaos Space Marine arms.
At first, I thought they might be recasts of the 2nd ed. plastic Chaos Space Marine arms, so I compared them, but they're actually distinct sculpts from those. I then tried to find them in my old Citadel catalogues, but no joy there. I then turned to The Stuff of Legends; nothing. Then on to Collecting Citadel Miniatures: nope. White Dwarfs and codices? Nada...
I finally gave in and sent the seller a message, asking about them and his answer was that the arms were initially metal, but they were very quickly changed for a plastic sprue.
So; can anyone confirm this story? I've never encountered or even seen such arms before. They're not in any White Dwarf, catalogue or flyer that I own. My guess is that they might have been some studio test bits perhaps?