The sled was just during the recommended break in I personally can't stand them. I'm with you thinking something between 180-200 would be great but have had no luck. Although the best so far was the Barnes LR 190gr as usually it will put 2 rounds within an inch and the 3rd will be further out and that's with letting it cool between every shot.
In my experience, when I see this, usually it is the shooter not the gun. I see it more often with lightweight guns in heavier recoiling chamberings as well.
If the barrel is properly stress relieved, which Brownings tend to be, it won't walk when hot. I have an A-Bolt II Stainless Stalker in 7-08 that I can get the barrel hot enough to cook on and it will still stack shots.
Do you have a lighter recoiling rifle, like a .22LR, .223, or 243? If so, try this:
1. Shoot one round out of the X-Bolt. Set it aside.
2. Shoot a five-shot group out of the other rifle.
3. Shoot another shot out of the X-Bolt
4. Repeat until you have a five-shot group out of the X-Bolt
If it is still 2MOA then it may be the gun or the load. Yes, this will take more time and use up some ammo in the other rifle, but it should help to mitigate recoil anticipation on the part of a shooter. YMMV.