I have used up to 4.7 gr of W231 for 158 gr LSWC, but that is considered a +P load according to Speer 13. I do not have a great deal of experience with W231 in 158 gr 38 SPL because my revolver does not shoot well with W231 loads and 158 gr LSWC. I have had better accuracy with Unique and heavier bullets. Conversely, I have had excellent results with W231 in lighter jacketed 38 SPL bullets such as 110 gr and 140 gr SJHP or SJSP.

My 2nd edition of Lee's Modern Reloading shows the maximum W231 load for 38 SPL LSWC to be 4.5 grains producing a pressure of 15,800 psi (not CUP), and a velocity of 830 fps. Speer 13 shows 4.3 grains max.