One addition on the Römerwerk (or Roemerwerk, if your keyboard like most is Umlaut-impeded). I wrote above: " The company details have been tentatively (but not really in-depth archivally) researched and have been partially documented in the "Germanhuntingguns" website, founded by Dieter Apel, rebuilt and mainted by Larry Schuknecht."

The last and possibly the most thorough research on them is hidden in a rather unlikely place. But it's six pages of text, hence not exactly short. Here:
https://portal.dnb.de/opac.htm?method=simpleSearch&cqlMode=true&query=idn%3D1294783467

And here is its table of contents, see pp. 10-15.
https://d-nb.info/1294783467/04

Carcano