For what it is worth, you may want to baby this thing through it's first 200 rounds or so, and give it a chance to let it brake in. Always use good ammo, and good mags though.
I have an Oly and it was cantankerous to say the least at first. I xcalled them with some of the same problems, and they reccomended a brake in period of up to 250 rounds. They were right!, and it didn't take that long either.
This may save you some time and shipping money, and Bushmaster the trouble of fixing soimething that is not really broke.