In general I've found that if you use the data in Speers manual you will come very close to the velocities they publish within the variation expected from using different guns. Use a Winchester primer rather than the CCI and a 4" revolver will deliver what they say a 6" will do. Speers data I have says 5.2grs of Unique is their max +P load in the .38 spl with the 135gr GD for 988 fps.