125 gr loads were associated with cracked forcing cones in the Model 19, etc.

I've heard it attributed to faster bullets, and I've hear it attributed to shorter bullets allowing the hot gas to get past the bullet and pre-heat the forcing cone. Neither is correct.

Erosion of the forcing cone creates V shaped cuts in the forcing cone, and those V shapes cuts become stress risers. In the K frame the forcing cone is milled flat on the bottom to allow clearance for the crane. That thin spot in the forcing cone is then more susceptible to stress cracks caused by the cuts from the erosion.

Erosion is maximized with large charges of colloidal ball powders - which happen to be the powders that produce the most velocity in the .357 Magnum when using longer barrels. The partially burnt powder flows through the forcing cone along with theft plasma from burnt powder, and the combination of heat and abrasion causes erosion to a much greater extent than with a faster burning flake powder.

The use of these powders occurred around the same time that law enforcement adopted the 125 gr hollow point. Around the same time several law enforcement agencies got sued for "under training" their officers by using .38 Special for practice and .357 Mag for duty. Consequently, most agencies stopped training with .38 Special and instead started training with their .357 Magnum duty loads. The Model 19, with it's thin forcing cone was designed to be shot mostly with .38 Special and only shot with .357 Mag on rare occasions, and was not designed for a steady diet of .357 Magnum. When a few Model 19s suffered cracked forcing cones, it wasn't really a surprise.

The lighter 125 gr bullets got the blame for the forcing cone cracks, but it's only partly deserved and needs to be qualified based on the powder used. For example, most 125 gr loads use a use a charge of around 20-21 grains of a slower burning colloidal ball powder like H110 or Win 296. That compares to around 16 grains of the same powder for a 158 gr bullet. This means that there is 20-25% more powder in the 125 gr load, and thus 20-25% more erosion per shot than with a 158 gr bullet.

Bullet weights lighter than 125 gains don't burn those slow colonial ball powders very efficiently, so they are seldom used and you don't see the same erosion and cracking issues with 110 grain loads - but no one really thinks about that.

You also don't see anywhere near the same level of forcing cone erosion with a flake powder like Unique. Those faster burning flake powders also produce comparable or even higher velocities in short barrel .357s. And with comparable bullets at comparable velocities, the faster powders (with charges around 9 grains - less than half the weight of a comparable load using H110/Win 296) produce significantly less recoil.

----

Now, with that said, I don't recommend a steady diet of .357 magnum for any K frame revolver - they simply were not designed for it (and neither were the J-magnum frame revolvers). But if I were going to subject a J or K-frame revolver to a steady diet of .357 Mag, I'd use a brand that did not use a colloidal ball powder, and failing the ability to control that, I would limit the bullet weight to 158 grains to reduce the amount of powder flowing through the forcing cone.