more research, XR3 and XR3-RED grip frames

[Fox Mike]

Single Six Magnum, SN 410851, ship Feb 65 (per Ruger), Has a "G" (actually raised rather then stamped) and solid pin but no "Alcoa" is visible with a 20 power glass.

 

[chet15]

Single Six Magnum, SN 410851, ship Feb 65 (per Ruger), Has a "G" (actually raised rather then stamped) and solid pin but no "Alcoa" is visible with a 20 power glass.

Did Ruger letter this gun for you as RSSMW or RSSMX?
If RSSMW, you've got a rare gun there and what would be considered the highest known of only a few known.
Chet15