Microstamping, in theory, would mean all pistols sold by licensed dealers would stamp a code on ammunition casings when fired that would include data like the make and model of the pistol, plus the serial number. That code would, in theory, allow police to connect spent casings at crime scenes to the gun that fired them, though it has never been tested in the field. All the character representing this information would have to be imprinted in the primer of the casing by the firing pin on every round. Not only that, but these character would have to remain perfectly legible after thousands of rounds. It would also mean replacing a firing pin on a given handgun would be nearly impossible.