I have used IMR4227 for 20 years with great success in the 41 Magnum. It works very well with both cast and jacketed bullets, best accuracy in the 1100 fps range with 210 grain bullets. It works so well with cast bullets that I rarely if ever fire a jacketetd bullts.

IMR4227 should work very well in the 357 in the same velocity range. I have tried it every now and then in the 357 with jacketed bullets, but have yet to find a load to equal my results with Unique, Lil Gun or H110. I suspect that this powders niche is 158 grain hard cast bullets in the 1100 fps range.

Checking Lyman Pistol & Revolver Handbook 3rd Ed., I find 2 cast bullets in the 150 to 160 grain range which list IMR4227 as their accuracy load, both the the 1330 fps range. Those are some pretty hot loads and my experience is that this powder works best at about 1100 fps.