RE: Triple shock X-bullets
What weight bullet are you using? What is the twist of your barrel? I'm thinking that either you're using heavy bullets and the rifle is just barely stabilizing them. Try a different weight bullet.
I'd also thoroughly clean the barrel with a good copper solvent like Barnes CR-10 or Sweets 7.62 (just don't leave either in the bore more than about 5 minutes, as they both have LOTS of ammonia that can, with a long soak, pit the barrel). Then try them again.
If that doesn't work, then it's quite possible that your rifle just doesn't like the TSX bullets. The Nosler BT's work well (they've always been very accurate in all the rifles I've tried them in), you could just stick with them unless you need a bullet that will provide more penetration. In that case you might try the Nosler Partition or the Hornady Interbond.
Good Luck,
Mike
When I had my .300 WSM I handloaded 180gr TSX bullets exclusively and they shot about 1.25 MOA average.