So the idea, if I understand, is that the firing pin would essentially "stamp" the serial number on the primer. A few thoughts immediately jump to mind:
1. A number is useless without a list to compare it to. So, for this to work, you need a database of numbers to refer to. Which means registration of all firearms.
2. If we're talking about microscopic stamping, isn't this also something that could be defeated by simply rubbing the face of the firing pin with sandpaper far a few seconds?
3. If the pin has to be "serialed" to match the gun, wouldn't repairs or replacement parts also have to be controlled and restricted?
4. Is there a grandfather clause in any of this legislation, or will any old gun become illegal for lack of an appropriate firing pin?
5. What about rimfires?