Well Zella Mehlis is located in what used to be East Germany. I expect the most notable firm that was located there until wars end was Walther which relocated to Ulm where they remain today. I drove thru Zella Mehlis when I was in Germany 2 years ago and couldn't find any remaining traces of gunmaking there.I suspect that lack of any detailed markings on your beautiful shotgun points to Guild construction.
Congradulations on a nice find!
Jim

The 2nd Amendment IS an unalienable right.