Some/many/most AR type firearms (and indeed many kinds of mechanical devices) need a bit of a "break in" period when new. In the AR's IMHO I would recommend first, cleaning the rifle well (particularly the BCG), field strip and clean off the typical "storage" oil. Lube a bit more than normal with a lighter weight oil (break free works well), particularly around the contact areas of the bolt, gas rings, extractor and ejector, and especially the cam pin. Also make sure you have some lube on the sliding surfaces of the bolt carrier and mating area inside the upper receiver, as well as the bottom surface of the bolt carrier and matching area of the hammer face. Next you just need to shoot it... most AR's should be broken in and running smoothly after 200, maybe 300 rounds.