WHAT DOES BCM LOWER MEAN?

bcn complete lowerAppeared it above so again and again and will't locate the blem. Everytime I think I discover anything off, it is simply oil smudges. Most effective guess at this stage is scuffs on castle nut, or The 2 very small silver spots from the flare from the magwell. 1mm dots at most. BCM QC isn't going to mess all around it seems.To my d