My Lee load data Remington .41 Mag is 8.0gr or 8.1gr starting load for W231 and 210gr JHP.
I am making some to shoot next month. There is a "lot" of unused space with the W231 load in the .41 mag.
H110/W296 or Lil'gun is more common, but more high velocity rounds.
I have been looking into a powder that is low velocity, but fills up case, and has other good characteristics(clean burning, etc.).
A friend uses dacron filler. I told him about the cream of wheat trick, so he is trying that.