In the Hornady #9 manual, the 357 Magnum pages recommend 5.0 gr. Unique as a max load for their swaged 158 gr. bullets @~ 950 fps from
their 8 in. Colt Python. 4.0 gr. is supposed to give ~ 800 fps. Loading 148 gr. wadcutters, the manual sez use .38 Spl. data. Of course, Hornady .38 Spl. data is for their swaged HBWC.