I put a lot of load development and testing to work up a suitable load for my open top.
Tried a number of different bullets/weights and powders.
Finally arrived at the magic combination, for my gun at least:
LSWC 240 VV N320 Gr. 5.8 LO: 737 HI: 766 AVG: 755 ES: 29 SD:8.00 PF: 181 RM Colt:
Shoots exactly to the sights at 25 yards and accurate enough to shoot the rope holding Tuco's head at 50 yards:
Not sure which model the OP has, but the Richards-Mason has the rear sight notch in the hammer.
1872 is different. Don't know if this makes any difference.