WK was the well known barrelmaker Wilhelm Kelber, Beiersgrund 3, Suhl. RS stands for Richard Schüler who ran the August Schüler company, Roschstrasse 13, Suhl, from 1913 – 1945. Richard Schüler (spelled Schueler also) was the designer of the "Herkules- action" and the Schüler cartridges 11.2x60, 11.2x72 and 12.7x70 aka .500 Schueler. Schueler made many bolt action rifles for the trade (= retail by others) too.