Aren't all BCM barrels chrome lined? I've never heard of a BCM built upper that choked on any type of ammo; enjoy the build. I was just comparing a KMR and NSR rail on my bench, and the NSR is hitting the sale block... the machining is mediocre at best when compared to the BCM.
Now get that A2 flash hider off there, mount your suppressor and then tell us how it runs.