Thank you Lancaster, interesting; Herr Charles 'Chas.' Heyer did not import in East Africa only Mauser rifles but also Mannlicher Schoenauer ones, and probably also many other types of German/Austrian weapons, such as this shotgun. Interestingly also, this shotgun may have been produced/named for the African market; the rationale for my assumption is that 'simba' means lion in Swahili (African native language spoken allover East and Central Africa) and I could not see this alien name being a selling added value for the German domestic market.
I don't forget that I have promised to scan and disseminate the Charles Heyer book I acquired some time ago, however I am currently working on a project abroad and will do it once back home.
Louis