Don, can you post an image of the Nitro stamp? Curious what the Prima Stahl - Bismark Stahl might have been? Some left over Bismark steel? The tubes were either by Gebhard Helmuthäuser or sourced from the Carl Gottlieb Haenel facility. Anyone now if any other Haenels wear Bismark steel? The lower tube is of Krupp steel.

Kind Regards,

Raimey
rse