I'm looking for the (not necessarily definitive) legal answer to a possible contingency, and I'd like to hear all educated opinions on this. We all know the serialized part on an AR-15 is the lower. What follows is a hypothetical scenario. Suppose that: 1) I buy a AR lower and get it legally transferred to me, standard ATF procedures and whatnot. I now own a "rifle" that is essentially a forged/milled hunk of metal. 2) Some time the in future, Congress passes some horrid feel-good legislation that instates a ban on certain firearm features (similar to the defunct '94 Assault Weapons Ban), such as telescoping stock, pistol grip, etc. However, pre-ban weapons are grandfathered in. In this scenario, is my previously-purchased receiver grandfathered in? That is, am I allowed to acquire and install these banned features on my AR lower, given that the "rifle" itself was acquired before the ban, and the rest of the parts are non-serialized, and therefore just "gravy"? If this is a valid train of logic, then it would be a good option for cheaply guaranteeing oneself future access to an "evil black rifle" for a low cost of investment today. Thoughts?