it depends. my 20" is zeroed on the m855 and really likes 68gr .223 as well - but all i had last time were 6 packs of hornady frontier 55gr match and it worked amazingly well at 300yds - after adjusting the drop amount it did group quite nicely and consistently.i like watching people dial in their optics with random ammo
steel tula was a waste of time, with steel wolf i had some better results, as of taiwan made cheap brass - did not have any lately.
the usual green tip imi m855 also groups reliably enough. all in all, with the 55cpr+ prices on proper ammo, and with match rounds sitting closer to 75cpr - it does not make it too easy.