On Blackhorn 209:
Did some checking around, and decided to start with 33.0 grains under the 500-grain Lee bullet. Three variations on this:
Resized cases*, wad under the bullet.
Resized cases, wad under bullet and about 1/4 sheet of toilet paper under that as filler,
Black powder cases, same filler.
All worked. The group with resized cases and the filler grouped better than without filler; the black-prepped cases a bit better yet. According to data gathered, I can safely increase the charge up to 35.0 grains**; that would eliminate the need(such as it is) for a filler, and I'm going to work up to it.
Velocity on those loads was very close to that given by the compressed charge of 2f black. With, as noted a couple of days ago, no need to use a blow tube between shots, or wipe the bore every five-ten. The wiping being a pain because you have to remove the tang sight so the cleaning rod can go in.
Some vertical stringing with some loads(couple of black and Blackhorn), which- until I can try them again- I'll have to blame on myself; the velocities were fairly consistent on the black, very on the Blackhorn, so almost certainly my fault. If there were a simple way to put a scope on this rifle for load testing, I'd do it to eliminate such error as much as possible.
So that's the results on that. Spent a little time after the shooting was done scrounging for brass, and I've got to finish processing that stuff. And loading some other stuff. And more .45-70 for next time.
*I only resize the first half-inch of the cases; that works the brass as little as necessary while providing consistent neck tension on bullets.
With cases intended for black, I don't resize at all; only flare the case mouth enough to allow the bullet to slide in cleanly.
Both of these work because the cases are being fired in one rifle, so don't have to worry about any chamber differences between different ones.