Because 777 is a constant burning powder and when you get over 110 gr you start blowing some out the barrel and BH is a progressive burning powder which burns according to how much pressure is created you will find the real difference what they can do over 110 gr; up to that point BH and 777 FFF are quite similar in velocities although some of us find a major difference because of crudring and I find a big difference in accuracy potential.