Snagged from wikipedia's Single Action Army page, so take it as you would any google search:
"From 1875 until 1880 Colt marketed a Single Action revolver in the .44 rimfire Henry caliber in a separate number range from no. 1 to 1,863.[5]
A "Flattop Target Model" was listed in Colt's catalogs from 1890 to 1898. Colt manufactured 914 of these revolvers with a frame which was flat on the top and fitted with an adjustable leaf rear sight. The front sight consisted of a base with an interchangeable blade.[6]
In 1896, at serial number 164,100, a spring-loaded base pin latch replaced the cylinder pin retaining screw and by 1900, at serial number 192,000, the Colt Single Action was certified for use with smokeless powder.[3] In 1920, larger, highly visible sights replaced the original thin blade and notch. The revolvers remained essentially unchanged from that point until cessation of manufacture at the beginning of World War II.[4]
From 1873 through 1940 (with small numbers assembled during and after World War II, the so called "Pre-War, Post-War" model), production of the Colt Single Action Army reached 357,859. This is identified as the "Pre War" or "First Generation" of the model. Calibers, at least thirty in all, ranged from .22 rimfire through .476 Eley, with approximately half, or 158,884 (including Bisley and Flat Top Target variations), chambered for .45 Colt. The next most prevalent were the .44-40 Winchester Center fire (WCF) at 71,392; 38-40 (38 WCF) at 50,520; 32-20 Winchester (32 WCF) at 43,284 and, the 41 Colt at 19,676.[3]"