Would love to duplicate the factory loads. Anyone have any idea as to what powder they use. I would guess it's Norma since they load the stuff and probably pretty fast burning since they seem to use about 66 gr.
I recall reading somewhere (can't remember where) that Norma used MRP in .257 Weatherby ammo. Don't know if that was for all loads or not. Can't find Norma powders around here locally. Personally, I've had very good success with H4831 and 117 grain gamekings.