JC is spot on and it is an Outstanding Quality touchmark used from say 1950 to the early 1970s. You have a proof date of February 1961 and note the Weichlot stamp, adjacent to the GM in a shield, which notes a tube joining method patented by Brothers Merkel:





http://www.doublegunshop.com/forums/ubbt...true#Post162485

I'd like to see if there are any initials on the tubes? Maybe just above the GM in a shield

Kind Regards,

Raimey
rse