Serial numbers can still be obtained from a weapon even if they are filed off. The stamp deforms the metal below the actual indention of the numbers which can be revealed using some kind of technology. (can’t recall specifically what it is)
Yeah, but the grain deformation doesn’t go that deep. If instead of filing or grinding, you used an end mill in a mill or drill press and went in 0.100 or so, I don’t believe that tech would work.