The M27 was the Registered Magnum that was highly hand finished but at a premium price.
Not quite. Here I am being a school marm again. Folks make these kind of statements all the time. The Registered Magnum was the Registered Magnum. Period.
Smith and Wesson introduced the 357 Magnum cartridge in 1935, and the N frame revolver that was designed to shoot it was simply called The 357 Magnum in the catalog. This cartridge and revolver were a further development of the 38/44 Outdoorsman and 38/44 Heavy Duty, which were N frame revolvers chambered for 38 Special and meant to fire the 38 Special High Velocity rounds. With the slightly longer 357 Magnum round it would no longer be possible to accidentally put a 38 Special High Velocity round in a standard K frame 38 M&P, which would probably have blown up the revolver.
Anyhoo, S&W started a clever marketing plan where each new 357 Magnum revolver would be registered at the factory to the owner. The gun was stamped on the frame under the yoke REGXXXX, and the number would be registered at the factory to the particular owner. These were the Registered Magnums. The Registered Magnums were custom guns. Each one was made to the owner's specifications. The owner could choose from 23 different barrel lengths, 6 different types of sights, Blue or Nickel plated, either finish could be engraved, and standard service grips or Magna grips. And of course, the top strap and barrel rib were checkered.
S&W never expected the Registered Magnums to be a high volume item, it was the height of the Depression after all. The cost of a Registered Magnum was $60, $15 more than any other revolver in the catalog. That was a lot of money in 1935. But S&W was overwhelmed by the response. The factory could only turn out about 120 Registered Magnums per month. By 1938, after building about 5,500 Registered Magnums, the registration program was dropped. The revolver continued to be produced right up until 1941, but they were no longer Registered Magnums, they were simply The 357 Magnum. The custom stamping of a Registration number on the frame was discontinued, and the amount of options available was reduced.
The 357 Magnum was reintroduced in 1948, with a new short throw hammer and the modern hammer block.
In 1957 Smith and Wesson changed over to the current model number system, and The 357 Magnum was renamed the Model 27.
So The Registered Magnums evolved into the Model 27, but they are not the same thing.