According to Brian Pearce's article on 1885s in the Rifle special edition, Single Shot Rifles and Cartridges his Low Wall grouped four Remington factory lead 255s into 1.10 to 1.70 at 50 yards. Handloads did better, and were still about that tight at 100.
For some reason, all the .45 Colt rifle data I've seen stays well below .44 mag data in the same guns. All I can figure is that the larger case makes the steel thinner under the barrel threads. Not to worry, Pearce has taken numerous big critters with 900-1000 fps loads in SAAs and the like, up to bears and elk. I've shot powder-puff loads in my .44 and they group well, but at least a foot higher than full-power ones, so when my supply is gone, I'm bumping them up.
That special edition magazine is a must-have for SS fans. Talk about eye-candy.
