HI TAC,
over the years I have tried lots of loads and bullets,
I have found that with the Lee cowboy type moulds a softer bullet works best,
10% alloy or a close guess,
tried hard alloys in my Sharps and big bore Wins,
no where near as good as the 10%,
may be the bullet expands into the grooves more being soft,
either way it works for me,
cheers T,