For a SD load (Wife carries a .357 Blackhawk in her purse) I use 18.0 grains of LIL'GUN with a 158 grain Speer Gold Dot. I get 1475 fps from a 4 5/8" barrel with that load. Not super accurate, but at short ranges it'll do.
For just paper punchin' I use HS-6 with whatever bullets I have handy, loaded down to about .38 Special velocities. I cast the 150 grain SWC with the LEE mold and also the HP version.
A year or two ago I did some experimentation with .357 mag loadings using various length barreled Colt Pythons. Trying to find the most accurate load for each of the barrel lengths. I don't have the exact loadings in front of me, but in general it seemed that the type of power used made a bigger difference then the actual amount of powder.
In the 8 inch barrel Python, 2400 seemed to give the best groups. In a 6 inch barrel, Power Pistol won out. In the 4 inch barrel, HS-6 worked best. I don't believe I played with the 2 inch barrel model then. Ran out of time and the mosquito population was beginning to bloom right around then. It is darn difficult to concentrate on your site picture when three mosquitos are heading right for your face.
Interesting thing was that as an average, HS-6 produced more consistent groupings than any other powder across the different barrel lengths. So if I were going to load up general purpose .357 mag bullets, not knowing exactly what gun I would use them in, I would use HS-6 as a preference.
BTW, this was using 125 grain jacketed projectiles and CCI magnum primers. Casings were mixed, but mostly Starline.