First, S&W did not envision the K-frame 357 Magnum as every having a steady diet of magnum ammo. It was designed with a concept of 38 Special ammo being used for practice and magnum ammo used for sight in, qualification, familiarization, and carry.

Second, at that time, the 158 grain bullet was the standard weight in 38 Special and 357 Magnum. The K-frame S&W revolvers were adequately durable with this bullet weight, especially if they did not have a steady diet of magnum rounds.

In order to understand the concept of the 125 grain loads, you have to examine bullet materials and design. The 125 grain SJHP 357 Magnum load was designed to get maximum expansion with adequate penetration. The 158 grain loads penetrated nicely, but usually completely penetrated and exited the average two-legged predator. The light weight bullets offered much more velocity, which made the exposed lead and relatively narrow hollow cavity of the SJHP bullets of the late 20th century expand rapidly, even forcing the jacket to expand. This rapid expansion also caused the bullet to quickly decelerate and reduced penetration. In order to get this velocity, a huge charge of slow burning, ball pistol powder was required. It is this huge charge of slow burning ball powder that is the cause of forcing cone erosion. When the erosion cuts deep enough, the thin, flat spot on the bottom of the K-frame barrel becomes prone to cracking.

With 158 grain loads, there is far less powder in the case, so there is less erosion with the heavier bullets.

Modern bullet design has overcome the need for blistering velocity. One of the more popular and effective bullets is the Speer 135 grain JHP. Speer makes this load in 38 Special, 38 Special +P, and 357 Magnum. It is taylored to revolvers with barrels of no more than 4 inches. The bullet has a very wide and deep hollow cavity and the jacket, which extends to and protects the edge of the cavity, is actually a fairly thick copper plating. These bullets expand very well at velocities that are well below what would have been required for older bullet designs.

In short, the time of the 125 grain full power SJHP 357 Magnum has come and gone. Advancements in materials have allowed reliable expansion to occur without the need for hyper-velocity.

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VCDL, GOA, NRA