From my experience with factory rifles and factory ammo, they all shoot different. What works in one rifle may not work in another. And they can change from lot to lot too.
To more directly answer your question... when I was shooting factory ammo out of my M77 7 RM years ago, Fed premium 160 NP's worked very well for me. Usually sub MOA. If I were to pick a factory load to experiment with first today, it would be Fed premium 160 AB's.
-MR