I'm not sure what powder you're using but for starters, I like using Titegroup for lead cast bullets. For my 38 special I use 3.4gr, 158gr cast LSWC, and a COL of 1.445". This should give you around 770fps +/-

For 357 magnum I use 4.9gr Titegroup, 158gr cast LSWC and a COL of 1.588". Use a tapered crimp on both, but not too aggressive of a crimp, just enough to get the bevel out of the case mouth and slightly rounded in. This load should get you around 980fps +/-