Uppers, etc don’t count as firearms. The lower is the firearm, and the part subject to the politician’s regulations.
Well, since I’ve been buildign ARs for a number of years, I am well aware that ‘the firearm’ is serial numbered and the parts that are not serial numbered are not considered ‘the firearm’. If you build a sound suppressor, you must get fedzilla permission BEFORE building the object AND put a serial number on the item. In the places where a slingshot is banned, is it considered a firearm?