A person I know claims that there is a way to run .308's in his AR-15 "just by changing the upper." I don't see how that's possible when a .308 round won't even fit through the mag well of his AR-15 lower, and I tried to tell him this, but he is insistent. If this were the case I'm not sure why anyone would be producing the AR-10/LR-308 guns? No, I'm not trolling, I just need some confirmation from folks who are more knowledgeable with this stuff than myself.