Steve-- I was thinking along the same lines. Having been in DoD procurement and security for over 33 years. The 3GM-K looks more like an office code that you see in the beginning of a military letter than a marking on the stock. Have you run across any of the Field Service or contact documents for Wright Engineering? Assignement of inspector's to Wright Engineering or government contract specialist. It seems logical that 3MG-K is a mystery and Wright Engineering is the only rebuild program for M1917 where we have no idea what the rebuild markings are. Additionally, the 3MG-K does not appear on any other weapon rebuilt for the government.