Title 18 Chapter 44 Section 922(r) of the United States Code, defined further by Title 27 Part 478.39 of the Code of Federal Regulation (CFR), restricts some imported semiautomatic rifles and shotguns to no more than 10 imported parts from a list of 20 parts.
As it applies to the FAL, to build a complete rifle out of an imported FAL parts kit no more than 10 imported parts can remain in the final completed rifle. In short, you must replace at least 7 parts from your imported parts and receiver kit with US-made components.
The below Compliance Calculator will help you determine if your FAL is compliant or non-compliant with Section 922(r.) To use it, unclick the parts you will replace with US-made parts and check the "TOTAL IMPORTED PARTS COUNT." Approximate prices and some US parts manufacturers are included.