Most data for the 357 Maximum is just that, maximum. I wanted to develop a cast bullet load for plinking and practice, and data for that was indeed scarce. I use H110 for my maximum loads and it performs wonderfully. But as we all know, you don't fiddle around reducing H110.
I tried something for the first time: I called the Sierra ballistics hotline, and they came up with 1 cast bullet load using 2400, from the Lyman manual. This powder, from St Elmer on down, had been "the" magnum powder, but unlike H110, it doesn't mind reducing the charge very much. They also had a 2400 load for the 180 gr SSP.
I've used the cast load and it's perfect for my purpose. I'm using Lee's 358-158 2R bullet, which weighs 165gr with my alloy, on top of an appropriate amount of 2400 and getting velocities in the neighborhood of 1600 fps, which is a very nice neighborhood !