Do you find the HS-6 to be a little dirty?   I used the EXACT same recipe as you for a while.   6.4gn HS-6 but was finding a lot of unburnt powder on the bench out of a 4″ Walther PDP.
Those RMR 115gn FMJ RNs are a treat though.   VERY consistent groups with that 6.4gn load.