Wayne, this is drifting some from the original intent of the thread, however:
I get 1650'/sec out of my 24" Jeffery .577 3 1/4" BPE with 178 grains (6 1/2 Dram) 650 woodleigh soft point. This with 100% Swiss 1 1/2F and Fed 215 Mag primer.
This is pretty much equal to the specs from the old days.
You did not mention what brand of black you were using?

As you know, every barrel is different. Try Swiss 1 1/2 and a Fed215 primer.
- Mike