I am going to put this stupid Bushmaster carbon fiber urban legendto bed for once and for all. I have a one, about 1 year old. Mine has the 16 SS fluted barrel, very accurate for a light barrel AR. I also have the following uppers that work great with it:
20" DPMS 223 1 in 7
11.5" DPMS 223 heavy barrel
5.5" 9mm, I can't remember the brand
20" DPMS 22LR
Everything functions great, no failures to feed or eject. That's 4 different bolt carriers. The only bad thing I can say is the design for the 6 position stock is a bit of a pain. Otherwise functions great. It weighs 4.3 lbs! I have a handgun that weighs more! Buy it and enjoy. It's a good base to add 223 uppers too. Check the photo section later this weekend.
My two cents.