[Unclenick]

If they are .454" LRN's then they are likely intended to be used as light CAS load bullets. A bullet that wide and light will scoot forward pretty easily under pressure, so you might actually do best with your quickest powder, the 231, to have something able to get pressure up quickly to bump the bullet up in the throat and be mostly burned before it clears the barrel/cylinder gap. I'd start at about 6 grains and figure to land on around 8 grains or so. Hodgdon's load data allows that powder to go up to 9 grains with a 160 grain cast bullet, and you could likely approach that, but the velocity will be getting to where you may be seeing leading issues before then. That depends on your bore dimensions, bore surface condition, chamber throat dimensions, etc.