I had good luck with the Lyman 275gr. gascheck bullet and 11.0gr. Herco in my Browning 1885 for a smokeless load. Of course BP works great too, at the speed range you're looking for. Also an interesting one is WC860 or other super slow powder, duplexed on top of 5% 4227 or somesuch as a compressed load. Basically BP performance but smokeless clean with very small single digit SD's.