I have a .300Wby in the ultralight weight configuration.
My rifle likes 2 types of bullets with the same powder charge.
Powder: Norma MRP - 84.5gr
Bullet: Barnes TSX - 180gr. or Nosler Accubond - 200gr.
I get my best groups with this powder and bullet combinations.
Having said that, I need to inform you that Norma MRP powder is not available in the U.S. anymore. I did read somewhere on this site that somebody else other than Graff & Sons is supposed to start selling Norma powder in the states again, but I don't know who that is.
If anybody has info regarding where MRP can be purchased, please let us know.
From what I have heard, Reloader 22 is supposed to be the same as MRP, except that the quality control standards for producing MRP are supposed to be higher. I have used Rel22 as a substitute for MRP, but I do not get the same groups as with MRP. Something is slightly different.
Also, Hired Gun, May I ask what your.257Wby recipe is. I have not had any luck getting mine to shoot with any bullet lighter than 115gr. My best .257Wby load is 70.5gr of MRP with 115gr TSX bullet. This combination gives me 5/8" groups.
Oh, one more thing, as stated previously, you do need forearm pressure on your barrel. Approx 14lbs, if memory serves me correctly.