I believe it was in 1893 when via an agreement that Krupp allowed Sauer to couple Krupp's 3 Ringe trademark on tubes of Weapons Grade Steel. So, by 1913 this was still a relatively new tube type and warranted @ least 20 additional Reich Marks on a scattergun. Krupp Stahl NIROSTA(Nitro Stahl - Nichtrostendender) was filed by Krupp on Oktober 17th, 1912 and a trademark in 1922-NIROSTA(NIchtROstendenSTAhl). There are 3 Ringe examples coupled with the term Nirosta.

Serbus,

Raimey
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