Even -- or especially -- Bill Jordan thought that the Combat Magnum (later, the Model 19) would be shot mostly with .38s, reserving .357 for serious work.
From
No Second Place Winner by William H. Jordan, written in 1965, talking about police cartridges. He thought the perfect police cartridge would be a .41 caliber, 200 gr wadcutter traveling at 1200=1300 f/s However it didnt exist, so .357 was the best extant:
The .357 Magnum is presently the best cartridge available. With the 160
grain bullet in 4-inch barrels it delivers slightly over 1200 F/S in the factory
loading and an authoritative 500 plus foot pounds of energy. While a little
more shock power would be desirable, no other available cartridge is so near
the ideal for police use. As an added advantage .38 Special loads can be fired
in the .357, thus cutting the expense of practice substantially. As a matter of
fact, it is probable that the average owner of a .357 Magnum will shoot
hundreds of .38 Special rounds through his gun for every Magnum round
fired. This leads to the conclusion that the lighter ".41 frame" revolvers
should be given preference over the heavy frame models. The S&W Combat
Magnum, for instance, is lighter and consequently more comfortable to carry
than the heavy Magnum. It has a faster, smoother action due to the difference
in cylinder weight. In effect, you have in one a heavy .357 Magnum which will
fire .38 Special loads, and in the other a light .38 Special which will fire the
Magnum load. While this is true of the .357 in which the recoil is mild
enough to be handled comfortably by the lighter weapon, it is most emphati-
cally not true of the bigger calibers. Here plenty of recoil absorbing weight is a
necessity to comfort and accuracy.
Note the loading he preferred, and the time frame he wrote this: heavier bullet, mid 60s. Also note that he thought the gun he designed was basically a .38 shooting .357 Magnums.
Steve Camp, RIP, former member of this board, studied and wrote extensively on handguns. While he was well known for his Browning Hi Power advice, he was also a revolver aficionado and had carried revolvers on and off duty as a police officer. Like many others, he really liked the K-frames.
He also recounts that police departments prior to the 70s liked to train their guys with .38s, but give them heavy bullet .357 ammo to carry on duty. He noted that about 1970 a couple different factors came together to change this practice: 1) lawsuits against police agencies for negligent training for using .38s in practice but .357s on duty; and 2) the advent of the 125 grain JHP, which had much different pressure profile than the traditional heavy bullet loads. Police departments changed their training policies, issued the new super cartridges, and suddenly Model 19s were shooting a lot more .357, in a loading that did not exist when it was first designed. Forcing cone cracks and other issues began cropping up. Not in all of them, but the numbers were significant enough that everyone heard about it. This very well may have pushed the K-frame to -- and sometimes past -- the limits its durability.
If memory serves, notice that this roughly corresponds to the introduction of the -4 version. I don't think one has anything to do with the other, just a coincidence of timing. In any case, Smith and Wesson introduced the L-frame, which had a beefier frame but the same grip dimensions as the K-frame, and the L's did not experience the same problems.
I have a Model 19-4 and Model 66, both inherited, and I think will stick to .38s. The 125 grain .357 is very unpleasant for me to shoot, and I don't want to risk any problems.