With the serial number obliterated from the butt, the only legal SN, the gun is contraband. Being found in possession of this you could be charged with a federal felony, and these are nothing to joke about! An obliterated SN usually the indicates the gun is either stolen or has been used in a crime. Can you think of any legitimate reason for this? There isn't any!

Attempt to get whatever you traded for it back and this gun back where it came from immediately. Failing this contact the local ATF Office having jurisdiction over your area. They will probably seize the gun and want to know where you got it. Whatever you lose on the gun is far less than even bail will be if you are arrested for possessing this gun, not to mention lawyers fees and fines or prison time which could be assessed to you. Best to be pro-active and contact them first.

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Gunsmithing since 1961