I have 2 Vanguards in 257 WM. Both love the Nosler BT 115gr in front of 69 grains of IMR 7828. This is not a max load but you do want to keep the Weatherbys near max as they seem to shoot better that way. Also, forget about loading them out near the lands. Buy a couple boxes of factory ammo and shoot them. Likely the Factory WEatherby ammo will shoot great. Then copy the COAL of the factory round. Weatherby/Norma knows how to load ammo for speed and accuracy.
Have fun!! Great round!
Michael
