The 257 Bee is not picky about loads. Any slow burning powder matched to the bullet weight will invariably give good groups and speed. I use what I can get hold of easily and that is 7828SSC. Meters well, top velocities with the heavier bullets I like and 1/2 MOA loads with 5 different bullet makes/weights. Most are so easy to load for they will shoot Weatherby Select factory ammo, at 40 bucks a box, into well less than a half inch for 3 shots. If it wasn't for wanting a different bullet than the 100 grain Hornady Interlock for Elk or Moose (it is a great bullet on Deer and Antelope but a little fragile up close for the heavier game), I would probably just use the factory ammo.