Jorge,
a 1:8.5” likely will do better with a heavier/longer bullet based on a lot of testing I did with 7 WSM loads for long range match shooting. Try a 168 - 180 grain bullet first before making a final decision. I used a 1:9” in 7 WSM’s, which produced best accuracy with 175 - 180’s in lead match bullets and mediocre groups with full power loads with bullets lighter than 160 in conventional cup and core bullets.
In Barnes, the 150 TTSX is longer, which is the factor which really is related to twist rate, and yet light to keep recoil down while providing high velocities Weatherby shooters like.
I also encountered bullets spinning out of jackets above 3200 fps in faster twist barrels. So perhaps try starting at lower velocity with the Partitions. A bonded bullet like an Accubond might better handle the higher velocity and twist rate if you like them. I ran a few tests runs with the 160 Accubond at a 1,000 just for the sake of trying them, and they could produce 2 MOA 10 shots groups at 1,000, which is not too bad for a “hunting” bullet.
The 7 Weatherby has enough more than enough muscle to push the heavy bullets at optimal velocities.
With the Sub-MOA guarantee, the range fee is absurd and likely a breach of their warranty.
Good luck, sorry for the frustrating new rifle. Hope it sorts out soon.
