3.7 Bullseye gave me great accuracy in my 6" magnums with 38 brass and a lead 158gr bullet. I never bothered with how fast it was going. For a +P of 890fps, 4.0grs of RedDot was most accurate at POA.

Winchester data has a 158 gr Lswc:
231, 4.7grs ........... 860 @ 17,100 psi +P

which was the 2nd most accurate in my two 6" magnums,
a mod 19 and 686.

Unique gets is best burn/accuracy at the higher end of 38 loads to the +P loads. I have NEVER found a GOOD light target load with this powder in a 6 or 2" 38 spl or magnum, yet....that faster burning powders could shoot in half the size.