pretty sure he was a local gunmaker in Harburg and this gun was made in Suhl or Zella-Mehlis.
Harburg is since 1937 a part of Hamburg when Great Hamburg was created, prior to that a city by its own.
A/E could mean "an der Elbe" - on the Elbe river.

you know the drill make pics of all parts and maybe its possible to say who made it.