You can alter the ballistics of a bullet by simply honing the barrel after you fire it, changing the distinctive scratches from the last bullets fired. This will only be a way of tracking stolen guns from stupid people and returning them to their owners before they get the stamps filed smooth.
I just don’t see someone with a plan to murder someone buying a new gun. I understand that some do, such as the case with the VT shooter. I agree with domenad on this, I can’t see how this will work.