FJS's 1959 Ernst Thalmann Werke Sauer example:













I'm guessing around 400k that Sauer changed to IZH crucible 4 Ring Special Gewehr Lauf Stahl and IZH had to began offering the steel type in 1951 because 1950 saw the last of the Krupp steel tubes and of course there may be exceptions.

Kind Regards,

Raimey
rse