Hard data being hard to come by. Depending on where you look, runs the gamut from "How dare you not use Holy Black in a .45-70!" to "Greatest thing EVER!", with little hard information of the "Here's a load that works wonders" variety.
I finally called Western and asked if it needed any compression like black: "No, you can have some space between powder and bullet, it won't get a pressure spike like back." So there's that. But I forgot to ask about actual maximum recommended charges. Yeah, sometimes I'm brilliant like that.
So we'll see what comes back.
I did some measuring, and found that 35.0 grains would let the 500-grain bullet be seated to the same level, and very slight compression, as with 68.0 grains of very-compressed black. So wrote to Western and asked about that load, they say that 35.0 should be fine, but don't go over that.
This is the kind of thing that makes reloading, ah, 'interesting' at times. The OAL they show for the flat-nose bullet is 2.515"; the oal I've been using with the Lee round-nose is 2.85" to put the bullet closer to the start of the rifling. Why the big difference?
I'm guessing their loads are intended to work in a lever-action repeater; with a single-shot, length is much less a factor. That also means, with the bullet seated further out, there's more space for powder. Blackhorn, I'm told, doesn't mind some empty space in the cartridge(as noted above), but 'some' is a very open-ended word here; yes, I'm asking about actual amounts. And giving some more information about the way I'm loading this cartridge to see of that affects the data(I know it does, but specifics would be very nice); for instance, having more space for powder, does that mean you can safely use more that if you were actually compressing it?
We'll see what comes back.