M855, all the way. M855 was designed to fight well equipped and armored opponents like the Russians and Chinese. Regular units of the Chinese Army are as well equipped/protected as our own soldiers. Im not sure how your AR15 is going to defend you against a Chinese SLBM or ICBM, but if it makes you sleep better at night, by all means....prepare. It would have to get pretty harry for a forigen army to occupy American ala "Red Dawn" and your best bet would be to flee. Even in the face of a strong and worthy adversary, the US military would ultimatly win. Our military superiority is such that we may take a small beating here and there, but we will ultimatly win. As Rome tought us, this wont always be so....but it will be for our lifetimes, god willing. Raise your kids right, and it will be true for thier lifetimes too.