I saw him thread a muzzle and priming rounds. It looks very much like they are getting 99% done guns and just assembling them, or making stocks or converting them to select fire, which happens in Mexico already. That's just a technical redefinition of what a "gun" is. However even if Mexico was forced to make do entirely with 90% lowers, it would still be a massive restriction in volume. The number of lowers is way, way smaller than the number of guns that are made every day.