Seeing your using Shockey Gold made by American Pioneer Powder company, they state, not to use lubes as it effects the powder. What I am guessing is your swabbing, and lubing with bore butter on the maxi effected the powder and you were not getting complete burn.

Try the same thing with some Pyrodex RS. Put in about 80 grains and try the Maxi Hunters. Personally I never had much luck with the Maxi Hunters. Now the Maxi Ball are a much better projectile for my rifles.

Also when I shot APP 3f, I never had good results shooting conicals. I get best results shooting light (under 300 gr) projectiles in sabots. The 240 & 250 grain did real good with APP.