Very nice shooting at 100 wiht open sights. What open sight are you using, factory supplied sight or did you put on a peep? To me the fact that the FPB is consistent, loads OK in your rifle and won't fragement on a close shot at 110g of 777 would lead me to conclude that FPB is best in your gun, but then again I am biased against PB based on personal experience. Honestly either would work well in your rifle. I recommend you also try the Blackhorn, it could shrink your group by 1/2 to 1", very consistent powder, and very clean--no swabing between shots.
Chap