Leopold Franz Oppenauer is/was still recently listed as an active gunsmith and gun shop in Ried im Innkreis, Upper Austria.
This is a prewar Ferlach gun retailed by Oppenauer, as suggested by Raimey in a more elaborate manner.
The set trigger indicates the gun also had another set of barrels, likely a shotgun/rifle combination or possibly a DR.

Kind regards,
Jani