Why would someone want a single action?
Howdy
Firing a revolver in single action mode is almost always more accurate than firing one double action. When firing double action you are compressing the hammer spring as you pull the trigger through a very long pull. That means you are exerting enough pressure with your finger to fully compress the spring. It is very difficult to keep the gun steady while yanking the trigger that much. With the hammer already cocked in single action mode, all you are doing with the trigger is pulling it back ever so slightly to release the hammer. The hammer spring has already been compressed, so it only requires light pressure on the trigger through a very short pull to release the pent up energy of the hammer spring. Very generally speaking, double action pulls are up around twelve pounds or more, single action pulls are down around three pounds or less. So accurate shooting is usually much easier in single action mode.
Why a single action revolver, when double action has been available for so long? Mostly it is just the romance of them. When I was a kid, Hoppy and Roy and Matt and Sugarfoot and Paladin and a whole bunch more cowboys regularly visited our living room through the magic of TV. Shooting single action revolvers brings back that romance.
As a matter of fact, it is probably all those TV cowboys that were responsible for the revival of the single action revolver in the first place. Colt stopped producing the Single Action Army in 1940 to free up production capacity for the 1911 Govt model semi-auto just before we entered WWII. At the end of the War, Colt probably had no intention of reintroducing the old revolver, they did not think they would sell many, and their prewar sales just before stopping production bore that out. But along came a young man named Bill Ruger, and around 1955 he offered up a little 22 caliber single action revolver, and they sold like hot cakes. He could not keep up with demand, and I'll bet a lot of that demand was caused by all those cowboys galloping through all those living rooms. Don't forget, that TV was still a luxury in a lot of households right after the war, but it was sweeping the nation. Ruger followed up with his 357 Magnum Blackhawk shortly after, and Colt got the message because in 1956 they reintroduced the SAA. They have been making it ever since.
The other thing about a single action revolver is the internal lockwork ( the parts that make it work) is much simpler than all the parts required to make a double action revolver work. That's why they are called double action. The lockwork allows the revolver to function in two completely different modes. Take apart a S&W sometime and you will see what I mean. There's a lot of parts in there.
Don't get me wrong, I love all my old S&W double action revolvers, and I have a whole passel of them. I love shooting them double action style too. But there's nothing quite like earing the hammer back on a single action for every shot.
And you would probably be amazed how fast a single action revolver can be shot. I know cowboy shooters who can empty a cylinder faster than most shooters can empty a semi-auto.