Loaded many thousands of cowboy rounds with Trail Boss and Titegroup, 4.0g with 180-200 grain bullets at about 650fps out of a 4 5/8 barrel. Have loaded .357's down to 2.0g. No experience with low velocity jacketed bullets but getting lead bullets stuck in a barrel with powder in the case is not a big concern. There is a point where some powders like 231/hp-38 don't burn up very well though. I don't know the lower limit but you do have to keep the bullet spun up enough to stabilize it and low velocity means low rpm.