I had a chance to load and shoot this rifle again.
This time, I used some of the GOEX Olde Eynsford 1-1/2F black powder.
I was able to load 80grs which is 5gr less than with the Shockeys because I am using an Oxyoke wad with the black and no lube with the Shockeys.
I also switched to a 350gr. Berrys Bullets .458" bullet which is similar to the Hawk but copper plated rather than copper jacketed. The bullets seat in the fired cases with some vigorous thumb pressure so no press seating was needed - nice!

Results at 75yds were good (for me)
The targets are sideways. First set of six shots on the bottom target and the last four on the top target (which also has two holes from a .45ACP carbine that look like a left and right flier) so the second group is pretty good I thought.
Just one swab with a wet patch between groups. Then I shot another eight shots without cleaning and kept clay target accuracy at 50yds.
I like this Olde Eynsford powder.