Chuck,

If I'm not mistaken, the "Fox Sterlingworth" is the dead giveaway to the Utica manufacture.

There was considerable variation in the frame radius long before Savage took over. I have a 1911 A grade with the large radius, a 1921 A grade with a 1/8" radius and a 1926 SW with no radius at all. Those are all Philly guns. Then I have a 1930 Utica SW with the 1/8" radius. I think the most that be concluded is that a very generous radius indicates a fairly early Fox....but even that may not be an absolute.