1936 versus 1936

[P. J. Heck]

Have acquired a second 1936. The one I have had for some time is #6723f w/match mag. It has the G date machining around the muzzle swell and a bright magazine body. The next one is #3622n, has the later approach to the machined angle at the muzzle swell and a blued matching mag. Lots of guns between f and n. two questions; what letter ends G date production??????? I have 4778d G date. What letter does 1937 begin with? I have 788r 1937 strawed. I guess the next questions would be what serial #/letter ended bright mag bodies and again for the muzzle swell machining change???