I've never personally loaded 38 SPL with either of those powders, but according to Hodgdon published data...
HS-6, start at 5.7gr (max is 6.3)
AutoComp, start at 4.8gr (max is 5.3)
I have used HP-38/231, and loaded 4gr with 158gr SWC --seems to be a popular load, but appears to be over Hodgdon's published data so you may want to start around 3.5gr.