From Reason:

The problem with imposing legal restrictions intended to stop a practice that is designed to evade legal restrictions is that you were outflanked before you even started. That’s the challenge for President Joe Biden and lawmakers around the country as they consider limits on “ghost guns”—homemade guns that are created, owned, and used off the government’s radar. Do-it-yourself manufacturing has always hobbled authorities’ ability to control things they don’t like, and the modern ghost gun movement specifically evolved to put personal armaments beyond the reach of the state.