In the past I've found that I have better luck finding an inexpensive ammo, shooting a box to see how accurate it performed in my particular AR and then, if I found a good one, buying as much as I could afford...
An example, several years ago when I was shooting a lot of 3 gun competitions and Prairie dogs, I stumbled on some Federal 50gr HPs that shot really good in the Colt AR with a 1/9 twist barrel that was being sold through WalMart in 200 round bulk packs...I bought 1000 rounds and still have a box or two in my storage. For some reason it failed in the accuracy dept in similar rifle with the same barrel length and twist rate. It still shot well but not to my needs for competition work..One of the primary reasons I started reloading..That allowed me to tailor the ammo to the individual rifle...