Heinz, it seems that it depends on who done the bluing, if the gun is striped and reblued then the link will be in the white, but if the bluing is an immersion type like the hot salt process, than the link will be blued also. I think.
In mid 1937 the hot salt immersion bluing process was used, but was the link included in this process or assembled after bluing?
Alf.