Hook - this info comes from old Winchester Factory load data that may not be available any longer as Winchester no longer loads the 200 gn bullet in either the 38 Spl or the 357. However, all you need do is substitute the 200 gn cast swc slug for the rn slug and
you are in business.
However, for as long as Winchester manufactured these loads these were the charges they used and the results posted::
38 Spl: 200 gn lead rn. 3.8 gn 231 powder, 770'/sec, 15.5K CUP. 7.2 gn 630 powder, 780'/sec, 15.5K CUP.
357 Mag: 200 gn lead rn. 5.5 gn 231 powder, 1060'/sec, 42.5K CUP. 10.8 gn 630 powder, 1270'/sec, 40K CUP. 12.4 gn 296 powder, 1335'/sec, 35K CUP.
HTH. Mikey.