RRA lower receiver with DPMS lower parts and DPMS bolt. The barrel I purchased from  friend new in the brown paper with a cardboard paper material in the bore.....markings as follows:
FNM1  MP  CHROME BORE. The number 7 is just visible forwrd of the chamber area of the barrel.
It was an easy build, the DPMS parts dropped in like it was made for it. Not one problem....now, I used a new bolt and new barrel, so what about the headspace?...thank you in advance for answering my novice questions......................