Thats crazy. No upper receivers have s/n's that I've seen. Wouldn't we need to file a form 1 as a maker if we had an s/n applied to the uppers?Read a little of HB205 and it sounds really bad for anyone who owns a rifle that has a lower & upper, only one of which is serialized, and any 80% frames/receivers that are not serialized from the factory. That covers a LOT of firearms, especially ARs.
This whole exercise is what happens when you let the clowns run the circus