Howdy
Funny you should post here on the S&W forum. Conversion revolvers, like those used by Clint Eastwood in Man With No Name did indeed exist in the Old West, and it is partially because of Smith and Wesson. Smith and Wesson controlled the patent for manufacturing revolvers that had the chambers bored straight through the cylinder so they could accept cartridge ammunition.
Prior to that time revolvers like the 1851 Colt Navy were what is called Cap & Ball revolvers. Self contained cartridges had not yet been perfected so most revolvers were loaded with loose powder and ball. A percussion cap was fitted onto a nipple at the rear of the cylinder. When the hammer struck the cap, it ignited sending a flame down to the powder charge, which then burned to send the ball down the barrel.
By the time S&W decided to manufacture their first revolvers in 1857 self contained cartridges were being developed. S&W had the bright idea to bore the hole straight through the cylinder so the newly invented 22 rimfire ammunition could be loaded. But when they did a patent search they discovered that a former Colt employee by the name of Rollin White had beat them to the punch and had already taken out a patent on the idea. S&W struck a deal with White granting them license to manufacture revolvers using his patented idea and they paid him a royalty of fifty cents for every revolver they manufactured. This deal remained in place until about 1872 when the patent expired. The upshot was that no other company, including Colt, was able to legally produce a cartridge revolver in the US until the patent expired.
The one exception I am aware of is Remington, which was licensed under the same patent to produce cartridge conversions of their Cap & Ball revolvers.
At the end of the War Between the States the US Army had thousands of Cap & Ball revolvers in inventory. They started selling them off as surplus at bargain prices. Many of these Cap & Ball revolvers found their way into the hands of veterans heading west. A lively trade sprang up with many gunsmiths in converting these Cap & Ball revolvers to shoot cartridges. This usually involved cutting off the rear of the cylinder where the percussion nipples were and fashioning a cap to go in its place. The hammer face was altered, usually to fire a rimfire cartridge. Cartridges similar to the 44 Henry Rimfire cartridge were usually used.
When the White patent finally expired, Colt was caught flat footed. They did not have a cartridge revolver in the wings ready to produce. Instead, they brought out several interim adaptations of their Cap & Ball designs. Here is a picture of the first of Colt's cartridge conversion models, the Richards Conversion which transformed the 1860 Colt Army into a cartridge revolver.
http://img.photobucket.com/albums/v4...conversion.jpg
By 1873 Colt had perfected the design of the Single Action Army, which was designed from the ground up as a cartridge revolver, but they continued manufacturing their cartridge conversion models for some years.
Today you can buy a copy of the Man With No Name gun from Cimarron. It is actually manufactured in Italy by Uberti. It fires 38 Special ammunition.
Man With No Name Conversion - Cimarron Firearms
Uberti is producing a fairly extensive line of revolvers based on both the Remington and Colt conversion revolvers,
Uberti 1860 Army Conversion, 1858 New Army Conversion, 1851 Navy Conversion, and 1871-1872 Open Top
In addition there are two companies, R&D and Kirst, producing conversion cylinders that can be fitted to existing reproduction Cap & Ball revolvers. I have two Italian made replicas of the 1858 Remington New Model Army that I shoot with R&D conversion cylinders sometimes in Cowboy Action Shooting. Here is a photo of one of them.
http://img.photobucket.com/albums/v4...htallsight.jpg
This revolver, by the way, is very similar to the revolver Clint Eastwood used in Pale Rider. In the big shootout scene at the end you can see him changing cylinders. He is using a gun rigged up by Hollywood propmen, but it is very similar to the conversions that Remington made to their Cap & Ball revolvers under license to S&W.
http://img.photobucket.com/albums/v4.../palerider.jpg