There is a new proposed federal gun bill in the House.
H.R 2910 says that it seeks to ban the sale and possession of 80% lower receivers for semi-auto rifles. An 80% receiver is not considered a firearm and still requires some basic machine work before it is ready to be used in the build of a gun.
The benefit of such receivers is that if you buy one and complete the work yourself, there is no need for the gun to have a serial number as long as it remains in your possession for personal use. It’s sort of a loophole in the current serial number requirement laws.