I don't know what world your on, but ar's suck at stopping the other rifles. I always have to use the scoped rifles now because thats the only solution i see to combat it after many failed attempts using a ar.
It reminds me of Halo 3 though, so im alright with it. Just alittle mad about the unlocking stuff by comendation, but i guess Reach made me used to collecting credits for armor.