Many cast bullets aren't right on the money weight wise anyway. 158gr data will do fine. FWIW, I have loaded allot of 158gr LSWC over the years using 3.9 +/- .1gr W231. These loads shoot well in near all my 38/357's. Low recoil. VG accuracy. Velocities in the low 800's.
A search here will give you lots of other data on this bullet and powder combo.

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Dave