Bcn complete lower Looked it more than so repeatedly and will't find the blem. Everytime I think I come across something off, it is just oil smudges. Best guess at this time is scuffs on castle nut, or the two little silver places during the flare of your magwell. 1mm https://bcm-lower46789.weblogco.com/28894814/considerations-to-know-about-bcm-lower-receiver