Well, I'm no expert but I have some information that may be of interest. My information here is through 1940 when it essentially went out of production for many years.
As I mentioned before, total production during that period was only about 310,000, not counting Bisley and target models, which was another 46,000 revolvers in round numbers.
Nearly half of the production was in .45 Colt. About 70,000 was in .44-40, 48,000 in .38-40 and 43,000 in .32-40. There were also another 20,000 in .41. All the rest were in two dozen other different calibers.
I would have to say the SAA retained a lot of popularity after 1910 and Elmer Keith would probably have had something to add to when he thought the end of that era was. However, you may be correct in guessing that the .44-40 was probably the most popular chambering for civilians, most likely because of the rifles that were also chambered for it.
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