The magazine well on your lower may be slightly undersize or the magazines may be slightly oversize. AR magazines are cheap. Sell, trade, throw out, or give away any that don't fit right, and buy some that do.
The 2nd Amendment was, and still is intended to protect the individual citizen from Tyranny. Whether that Tyranny originates from
our own Government, common criminals, Progressive Liberalism, or foreign invaders, is irrelevant.