Hello Folks,
I just received a Greener Empire double rifle dated 1928.



It's hard to see on my poor picture but there is "ZSR" stamped on the tube.
The Graham Greener letter mentions that the rifle was made with "ZSR" steel.
Does anyone has any idea what that is?
I googled a lot but got nothing.

Best regards,
WC-

P.S> Graham thought this gun might be one of a kind, but I know there is at least another one around.