I remember casting up some Lyman RNFPs at a nominal 300 grains. This was the original Lyman profile for .45-90, the #457191. I swaged them down to .452 and RangerBob and I loaded them up in .45 Colt brass for use in his Blackhawk, specifically for longer ranges. I do not remember the load data, but I do remember that the load was not a full-house one. That bullet turned out to be quite accurate in that application.

I do know that in your place, I would start with Unique. Whenever I'm looking for a good accurate load, Unique just seems to work.

-AaronB

EDIT: I found some online load data for 300-grainers in .45 Colt that you might use for a starting point... several of your powders are represented. You can find the data here.

In your place I think I'd start with 6.0 grains of Unique under your 315-grainer and work up from there. I tend to be conservative (I'm fond of my fingers and I'm not really interested in velocity for its own sake).

Brian Pierce wrote a recent article in Handloader magazine with maximum safe loads in the 45 Colt flattop. Best powders were VV N350 and AA#9.