Well, seems to me the OP's question is a reasonable one... if two revolvers are identical in all respects except for chambering - say an S&W Model 15 and an S&W Model 19 - why couldn't/shouldn't a handloader be able to load both to the same pressure levels?

And the answer is that they are not the same. They are both K-frames, but the metallurgy of the Model 15 is different from a Model 19.

Back in the day - during the 1930's when the .357 Magnum was being developed, for instance - that difference was mostly limited to differing heat treatments. Today, manufacturers are as likely to spec entirely different steels.

Metallurgy matters. And as that has improved over time we're afforded things some of us never could have imagined back in the day... like J-frame .357 chamberings, or L-frame .44 Magnums.

The bottom line is that the caliber roll-stamped on that barrel is more than just marketing. Load your rounds accordingly...