LarryL,
I'm shooting the Hornady "Varmint Express" ammo, 55 gr, V-Max. It's really accurate in my Remington 700 BDL varmint special, and does a good job for me out to 250-275 yards. Sighted in at 200 yards, the round is 1.4 in. high at 100 yds., and 7.1 in. low at 300 yds. It's about $12 per 20 round box.
At around the same cost, $24 for a 50 round box, Black Hills makes a pretty accurate 50 gr. V-Max Moly round that shoots well in my 1:12 twist barrel.
You didn't say what twist rate your AR barrel is. The faster the twist, like a 1:9, would stabilize a heavier bullet. The slower twist rates, like my bolt action rifle, does better with the lighter bullets.
TennSquire