[The lower is 80% complete. It doesn't need a serial number since it isn't complete.
You finish it on your own with a drill press. Can't resale it or make one for a buddy.
As long as it is your personal weapon, no serial # is required. If it ever leaves your possession (sold, gifted, or inherited), a serial number must be obtained from the BATF and stamped on the gun as required by federal law. I think you must keep the paperwork proving you are the original owner of the 80% lower as well. LEO's frown upon weapons with no serial number.
