The M27 is Smith's challenger to the Colt Python ? For a steady diet .357's, the 27 is better; but for carry, the 19 is better ?
The Model 27 is S&W's N-frame chambered in 357 Magnum. This is fundamentally the original and world's first 357 Magnum. As early as 1930, S&W produced N frames chambered for high-pressure .38 Specials that became known as .38/44. The "Registered Magnum," introduced in 1935 was an extension of that concept that was accompanied by the introduction of the 357 Magnum cartridge, which is just 3.7mm longer. Factory 357 cartridges were loaded to a higher pressure than factory .38/44, but handloaders like Elmer Keith loaded them to similar pressures (it is, after all, the same gun). Some say the 357's extra case length was to prevent it from being loaded into weaker 38 Special revolvers, like a K-frame hand-ejector. The other reason for the extra case length was additional powder volume. Since maximum peak pressure can be achieved in the smaller 38 special case, the advantage of more powder volume isn't simply more energy, but to allow enough space for bulkier powders that are more heavily covered in deterrent -- material that slows the combustion of the powder. We call these more heavily-deterred powders "slower." Slower powders allow more total energy to be delivered before the bullet exits the muzzle because they can keep the pressure higher, closer to the maximum peak pressure for a longer time. They create more area under the pressure/time curve. In "2020" terms, they "flatten the curve." In order to get the most out of this, a long barrel is needed or you run out of time and the bullet exits.
The Registered Magnum was S&W's flagship revolver, and the world's most powerful (production) handgun from 1935 until 1939. Every one of them was custom made to order and an extensive list of hand-crafted features was available. Upon completion, each was "registered" to the original purchaser. J. Edgar Hoover received the first one, and other famous people like General George Patton possessed one. They were remarkably successful as a luxury item in the midst of the Great Depression. In 1939, S&W stopped making Registered Magnums and started making the "357 Magnum," which was a regular production gun (not custom ordered). In 1954 they introduced the "Highway Patrolmen" which was plainer still -- lacking the "357 Magnum"'s top-strap checkering and polished blue finish. In 1957, S&W introduced its model numbering system and the 357 Magnum became the Model 27. The Highway Patrolman became the Model 28. 1957 was also the year S&W introduced the K-frame Model 19 in 357 Magnum. It was greatly preferred by people that carried a gun daily because the N frame was very large and heavy.
The Colt Python was introduced in 1955. It is smaller than an N-frame S&W, but bigger than a K frame like the model 19. The size is very close to the S&W L-frame (586 and 686 which weren't introduced until 1983).
S&W continued its production of the Model 27 until 1994. It lost the pinned barrels and recessed chambers in the cylinder by 1982. In 1989 they started producing stainless steel versions. I suspect they may not have called them Model 627 at first, but I'm not sure. They are certainly known as model 627 now. In 1996 they started producing 8-chamber model 627. In 2008 they introduced the Scandium-framed 327, also with eight-chambers. In 2011, S&W re-introduced the Model 27 Classic which is very similar to what they were producing when they stopped producing model 27's in 1994. The differences are the design of the rear sight, the presence of the hammer lock, and MIM parts like the hammer and trigger. Another difference is the barrels used to have broach cut rifling and now they are rifled by an ECM process. These changes, except the lock, are all improvements compared to 1994. I'm ambivalent about the lock. It doesn't ruin the gun, but it's hard to argue that it's an improvement. Overall, a Model 27 Classic is a better gun than a 1994 Model 27. When you go farther back, especially to pre-war Registered Magnums, there's really no comparison. Those were custom-crafted by artisans. They are revolver masterpieces surpassed only by the most elaborate custom jobs and they have historical and collector significance that no current production gun can possess.