The four rings separate "Special-Gewehr" and "Lauf-Stahl S.G.1" I have wondered if that stamp was somehow actually related to the material, or in imitation of the old three ring Krupp Logo.
Yes, 4-rings was related to material, according to some Soviet publications in press it was Russian barrel steel 50A (S.G.1).
But there is one question where did GDR get barrel steel when all pre-war and war time German steel stock got empty? Definatly from USSR. There were 3 types of Russian barrel steel for hunting weapons: 50A, later 50AR and chrome-nickel steel 30CrN2МF (Boler Blitz analog) mostly on GDR Merkel's and other high grade GDR guns.
The story with 4 rings "Krupp" steel is not quite clear. Guns for export to the West or because Krupp family was in West Germany and claimed ther rights for 3-ring trademark.
