I don't know how much time you have in revolver shooting, particularly single actions, but grip pressure and grip position mean a ton. Even off of bags you need to be consistant with the grip. Also when shooting off bags do not let the butt of the grip rest on anything. I use my standard field hold and cradle the frame, in front of the trigger guard, on the bags. It helps a lot and your POI doesn't change much when you go to off-hand. Takes practice, and more practice.