I agree with the last couple post on the 1/10 twist barrel for the 300mag. I think Wby found that out when they changed over to a 1/10 twist for the 300WbyMag vs using the 1/12 twist. Wby only has one load for a 200gr bullet but 6 loads for the 180gr and 4 loads 165gr and 2 load 150gr bullets for their mag.
If your going to build something maybe use 1 or two bullets you might do better with different twist but you sure want to talk to the barrel guys and get feedback from them also talk to the bullet guys. Nothing wrong with getting education from the guys who build them.
I tend to build around certain bullets.