I have no desire to get into a spitting contest- however. There are approx. two million threads here dealing with this- I have read them all- I still don't know the real answer. I attribute this to Colt's inconsistency with their product- gotta love 'em anyway. What I can tell you knowing it is 100% accurate is I have seen a MT lightweight (16" barrel, A2 fixed carry handle, 1999 production) come out of the sealed box from Colt with chrome bore and chamber. Barrel was marked "CMP 5.56 NATO 1/7". No possibility of error there. It also featured the sear relief in the upper receiver as well as the extended "M4" feed ramps- go figure. Hope this info helps. I would say figure out how to identify the features first and inspect the rifle before purchasing.