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Back before the First World War the Army sold off Colt Single Action Army revolvers by the barrel full as surplus, for scrap-metal prices. They sat around for years until the 1920s, when Hollywood studios needed cheap props. SAAs became part of the cultural expectation for Western scenes and now anything else looks weird.
 
Circa 1880, when men went armed on the frontier, their sidearms varied a lot. Colt had lots of competitors for the civilian market. Top-break S&W revolvers were very commonplace, as were cap-and-ball revolvers like the Colt Navy and the LeMat, at the time tech only a few years old. The fugly, ungainly looking Merwin & Hulbert revolvers were popular, but you never see them in old movies–because they weren’t available at scrap-metal prices between the World Wars for movie studios to buy up.
 
The Colt Single Action Army is a graceful and photogenic handgun, with beautiful lines. Those who have handled and fired them are not always so enthusiastic. They do not point the least bit naturally. The hand-fitted leaf-spring lockwork is delicate and fragile and prone to breakage. The fixed sights are an afterthought and all but unusable. The standard grip frame was copied over from the Colt 1851 Navy grip frame, and is in the modern era much, much too small for the hands of anyone over eleven or twelve years old and adults typically have to take a very awkward grip with their pinkies curled up under the bottom of the frame. John Wayne was a manlet.
 
But oh, they’re gorgeous to look at.
 

I know double actions absolutely existed during the time period, but I still have a hard time imagining westerns with anything but single action revolvers.