got a upper off a EE seller and it is stamped
NB 5.56 1/9 MP
any clues on the maker?
the upper is marked with an FK in front of sight.
Also barrel is an odd contour. I have owned Colts, RRA, DPMS, Bushy, Oly and some other off things including M1S and M&A stuff and none of them have had the contour this one has.