Still reading the ATF Definition of Frame or Receiver and Identification of Firearms and they go great length citing chapter and verse on some court decisions trying to prop up the idea that without serial numbers, crimes will not be solved, and we will be overrun with violent criminals shooting left and right. Of course, they fail to mention that firearms tracing in real life has very little to do with crime solving, especially homicides and that the only place where the serial number of a gun leads to the identity of the killer only happens in TV shows and Hollywood movies.
The only thing that the tracing of a gun’s serial number does is to find out who was the last legal purchaser of said gun through a Federal Firearms Licensee. Serial numbers are not GPS, nor recording devices that keep track of every action done with the gun. They are as effective in crime reduction as the numbers in your mailbox.
But they are damned good for confiscation purposes which is why the Government loves them so.