When any firearm, 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 graphene circuits, are x-ray undetectable, can easily be melted down to prevent ballistics tests, https://troymbmua.blogstival.com/36796779/high-production-produced-3d-printed-plastic-assault-guns-on-the-way