Powder and Bullet Advice for .257 Wby Mag

[ryalred]

NOTE: I'm posting this in the "Art of The Rifle" section as well. Didn't know for sure where it would produce the best results.

My son has a new .257 Wby Mag (Vanguard) and the ammo that shoots well in mine and my son-in-law's will not group well in his. We've been using RL22 with Hornady 117 grain interlocks and mine also shoots the 100 grain Sierra GameKings real well. I've tried a number of different charge weights with this two bullets but can only get about 1.5" groups at 100 yds. Mine and my son-in-law's shoots sub MOA. If you were going to try a different powder, what would be your first choice, H or IMR 4831? I'm thinking it is more of a powder problem than a bullet problem since it won't shoot the Hornady or Sierras very well; however, if you were going to try a different bullet, what would it be? I'm looking for tight groups and am not particularly worried about speed, as almost all loads for the .257 Wby Mag have plenty of speed for our whitetail deer in SE Oklahoma. Your advice will be deeply appreciated.