8 billion? That would require, mmmmmm, ten digits. Plus two for the year, I suppose. Maybe one more, to allow for production to reach ten billion.
Thirteen unique id digits. That gonna fit on a .22 short...???
Uh, no. That's why they will require all ammunition produced to be .50 BMG... just think of the brilliance... the serial number will fit... and the serial number will never get disfigured by firing because all .50BMG firearms are illegal!