1st...no need to use 150 grains of powder...Best groups will be between 85-110 grains of loose...Remember the 45/70 killed a lot of buffalo....

Bullet selection is also dependent on how far you will be shooting....If shooting open fields a 250 SST/Shockwave or a Dead Center stye bullet is a good selection...

If shots are within 100, a bullet like the 250 or 300 Barnes MZ, Hornady XTP, Speer, Nosler Partition works...Except for the Barnes which was designed for muzzleloading these are simply .451 handgun bullets that can be bought in bulk and matched with a MMP-12 or MMP-24 sabot, whichever is right for the diameter .50 caliber bore you have....

My Knight likes 90grs of Pryodex R-S or Goex FFF and the 250 T/C Shockwave....I'm sighted 2 1/2 inches high at 100 yards and I'm 2 1/2 to 3 inches low at 150, which is my max range....For several years I used the Barnes 300 MZ, and 100grs, but the Shocwkave shoots flatter, even with less powder....Good Luck...