When I switched to 20 ga, I had trouble finding a powder recommended for the 20. I found Winchester 572 locally and it specifically referred to 20ga.
I have used it for over a thousand rounds without any problems......basically 16gr, 7/8 oz. It may not get quite to 1000 or under but can get close.
Good luck,
OO
I believe that the blackhawk grip frame is the same as the Ruger single six "long" grip frame.....I think TR is looking for "short" grip frames for his single sixes.