An acquaintance of mine has been gifted a modern, US made, semiautomatic handgun. Somewhere in the handgun's past life, someone filed off the serial number. My acquaintance asked me what he needs to do to get this gun legal again (assuming that the present situation is not in compliance with some law). My only thought was to contact the manufacturer to purchase a new frame and swap out the components. Does anyone here have a better / more correct answer?