I think I know the answer, but I don't want to assume I'm right and just go ahead and do it. I have a Direct Impingement (Piston-Driven) rifle that I do most of my shooting with. I also have a Gas-Operated Upper sitting around doing nothing that I'd like to get some use out of. My question is, can switch out the uppers and put the Gas-Operated Upper on the Lower of my Piston-Operated rifle? I'm guessing the answer is gonna be yes because I can't see what difference how the upper functions would make to the lower, but before I just go ahead and do it I'd like to see if anyone here has done it and/or knows the answer.