I think if your asking about accuracy relating to ammunition manufacturers than I think that you have to try different brands and bullets within those brands and see what works best. Big Country brought up a good point and that is quality of ammo leaving factory if one were to look there than Weatherby Ammo(Norma) is the finest available followed probably by Federal and Hornady. I have been having real good results with Winchester Failsafe,Ballistic Silvertip and Powerpoint in a 270,300 wsm and a 308 lately bottom line your going to have to experiment .

If your talking inherent accuracy and meant for a big game rifle look at anything built on the 308(243,260,7-08,358) case or 06(270 280) case for starters. The 300 wsm,300 win mag and 7 mag,338 are all great shooters. Weatherbys because of that darn long throat tend not to be as accurate but that can be remedied in a factory cartridge. Antyhting bigger then the cartridges I mentioned than Others on this board that have experience with the larger cartridges can give their 2 cents.