I agree with Terry, the engraving looks "F". I note from the pics the side plates are the earlier style with attached sears & also a bearing for the hammer axle (hole just under the C in Co). This would indicate to me a gun no later than the mid 20K serial number range & likely a "Two Hook" cocker. At this point the G grade carried only a simple line around the edge of the plate & a bit of "Sunburst" on screw heads etc. I have a G in the 29K SN range & it has already gone to the large single hook, frame mounted sears, no axle bearing in the plates & lost the cross pin through the frame where it steps down to the rounded contour. It still has only the line engraving. Around the 40K/50K SN range a scroll pattern was added to the G's side plates, I have never seen another G with ant animal scenes in the engraving.
Is the G marked on barrels only, frame only or both. I am wondering if this gun started life as & F & has subsequently been re-fit with a set of G grade barrels.
