The most accurate bullet in my two .257s is the 100-grain Nosler Ballistic Tip. Not cheap - but highly accurate. It would "work" on game at extreme range, but is really too soft for the cartridge. For targets, it is great. On game I prefer the Barnes X bullets. They shoot well in my barrels and can't blow up. The 100-grains bullets are what made this long range cartridge's reputation.
The 85-grain BTip is a great varmint bullet and about as accurate as the 100s, but like 'most any bullet over 60 grains it can richochet over flat ground. I always shoot them in areas where I can see as far as a bullet may go, like tundra, plains, and rocky canyons. This is not a prairie dog cartridge afterall....