If you are pleased with your '19, you might want to look up the history of what was called (before Smiths had model numbers) the "Combat Magnum." Here's the quick version, but you'll probably enjoy doing more research than I can summarize here:
In the late 30's, some folks came up with a cartridge called the .38/44 or .38 Hi-Vel, which was a .38 special case loaded to higher pressures and velocities than industry spec. In part (or at least, in theory), the motivation came from law enforcement, which found the spec .38 special inadequate when used against felons fleeing in automobiles. (This, you will note, was before the Court held that shooting at a fleeing felon was a violation of the Due Process Clause.) (More likely, the .38/44 and later .357 Magnum were spawned by the 'druthers of a fellow named Keith, a civilian, who disliked any firearm whose recoil was too little to rattle his teeth.)
Smith & Wesson brought out an N-Frame (large frame) revolver called the .38/44 Outdoorsman, designed specifically for this cartridge. However, even in a 4-inch configuration, the N-Frame was a bit big and heavy to be carried around all day by uniformed police officers.
The .38/44 morphed into the .357 Magnum, which is a .38 special case lengthened 0.135" solely to prevent it from being chambered in .38 special guns (which might not be able to handle the pressures), and the Outdoorsman morphed into the 357 Magnum (shiny grade) and Highway Patrolman (matte version). They were big sellers amongst civilians.
A bit later a fellow by the name of Jordan (then director of the U.S. Border Patrol) spoke to a fellow by the name of Hellstrom (then president of Smith & Wesson) about chambering the K-Frame revolver (specifically, the Model 15 "Combat Masterpiece") for the .357 Magnum cartridge. Hellstrom was dubious, but he took the request back to the factory, where the engineers opined that with some changes in metalurgy and a couple of very minor configuration changes, a K-Frame .357 could be designed.
The "Combat Magnum" (later Model 19) was thus birthed.
You should be aware that S&W informed Jordan (and others) that the K-Frame should not be fed a steady diet of full house .357 Magnum rounds. As a result, Jordan instituted a program, dubious under modern notions of training, that his men would train with .38 special rounds and carry the .357 rounds while on duty.
As someone observed, with a pinned barrel and countersunk chambers, as your pistol has, it comes from the 60s or 70s, most likely during the period when Model 19s had increadily smooth trigger pulls.
I have two '19s, a '66 ('19 in stainless steel) and a '65 ('19 with fixed sights, narrow hammer and narrow trigger, also in stainless). I do not shoot .357 Magnum rounds through them.
