The Fed Ord I worked on wasn't mil-spec and was a mix match of military surplus (sights, trigge group, op-rod, bolt, op-rod spring guide, flash hider were all mil surp) parts and rejects. Specifically, the gas cylinder was particularly hard to unitize as it required turning on a lathe (had to figure out that the surface was canted). The receiver bridge was roughly casted (nothing I could do to fix that). According to the owner, the barrel also had a lump in a land (don't ask me how that came about), but the barrel was replaced with a surplus one prior to it be loaned to me for accurizing. It was a fun gun to learn on, but I'm glad mine is Smith Enterprise.