My carbine does best with bullets from 50gr to 60gr in weight. I've tried some 77gr Sierra Match King loads and wasn't impressed, never was able to get a 5 shot 100 yard group under 1 1/2 inches. I've had OK results with the 69gr SMK, just over an inch at 100 yards. If I were going to pick 1 bullet it would be the 60gr V-max, my carbine will group them around 3/4 of an inch consistently. The best groups come from a 55gr Sierra Blitz King and 52gr SMK, I get 1/2 inch 5 shot groups regularly.
As far as factory ammo I get very good results with Black Hills and with IMI ammo. The best varmint ammo I've used is Black Hills 50gr V-max and Fiocchi 40gr V-max.