Like silvertip-co and 375fan stated, HSM, Black Hills and others make premium (almost semi-custom) ammo. I tried those in my 6.5x284 hoping to have some long range fun without sinking a bunch into reloading gear.
It hovered around MOA in my rifle, but nothing spectacular. Not until I made the investment to get back into handloading did I get the performance I expected at 1k.
A friend wanted help dialing in his 300WM, but didn't want to handload. So, we chronied a box of superformance ammo. He was sub-moa at 100yds and the ES was less than 10fps. Even so, it would be interesting to see how consistent the ammo might perform across various batches and over time.
I've read that ammo companies often make subtle changes from batch to batch. I don't know how true that is. But, I have seen instances where a given rifle is very forgiving of certain deviations and very unforgiving of others. I have to assume that applies to factory ammo that is "manufactured to specs to go in all firearms" as 375fan stated.
On the other hand, I've heard of spectacular results using 6mm BR factory ammo from Lapua and Norma.
Factory-Loaded 6mm BR Ammo
I guess it depends a lot on whether your rifle likes it and the manufaturer's ability to maintain consistency.
--Richard