German factory that makes 460 Steyr brass from 50 BMG cases?

I have a new empy 460 Steyr case made from 50 BMG brass ( headstamp DM 43) . The guy who sent me this case, a gun smith, wrote me that he imported this brass from Germany for an italian shooter ( 460 rifles have just became available for italian shooters), but he doesn’t remember the exact name of the factory who made them.

Any ideas about the possible maker?