Can't go wrong with Vihtavouri N320 in either 38 or 357.

I use 4.8grns in a .357mag case with a 158grn TC lead bullet - and it will out perform me at 50 metres in my rifle, when I do my part it will single hole at this range.

4.8grns is a maximum .38spl charge for N320 with that head but below minimum in a .357mag. In general, max 38 loads are fine in 357 cases.

Andy