Everyone seems to have their opinion on the best powder for specific chamberings used in toggle link actons. After trying a handful of newer offerings for my 45 Colt I find myself back to good ole "Unique" for the 1866 Uberti Yellow Boy,....6.5 grs of Unique launching this 300 gr cast yields a consistent 1040 fps with no pressure signs and very good accuracy as long as my aging peepers cooperate.No fouling,leading, un-burned powder residue or even " blow back sooty cases" as are so many complaints with the Colt chambering not sealing well..My SOP for this load is a big bullet,good tight crimp and safely not going whimpy on the charge.

Universal may be a close second........