why would a crimal want a gun that can't be traced by a serial number?
have a gun made after 1968 in your Possession with out a serial number is a federal felony.( rather you filed it off or got in off a production line before it was serialized)
Why on earth would a crimal want to have a gun that if they are cuaght with is federal time?
Granted crimals are not always known for being smart, but still even a gang banger can figure that one out. You would get less time for a stolen gun, and it would be state time, not federal.