When any weapon, metal or plastic, is sold as separate components, such as sub-receiver, stock, barrel, scope, etc., they can serve non-weapon functions, and were never banned, and never can be. Plastic, even electro-magnetic guns with carbon circuits, are x-ray elusive, can easily be melted down to prevent ballistics tests, https://josueacxri.wizzardsblog.com/15672992/high-production-proliferated-three-d-printed-plastic-assault-guns-ramping-up