I suggest you go experiment with your 18" upper. Shoot it in it's current state of tune, paying attention to how sharp the recoil feels. Then, Now, put a single round in your magazine and load the rifle and shoot it. Keep closing of the gas until the rifle ejects, but does not lock back. Then, open your gas block one click and test to make sure the rifle ejects and locks back. Run 10 or 20 rounds through it, noting how the recoil feels. You'll notice it feels softer (unless you're running a carbine weight buffer. If you're running a carbine weight buffer, get replace it with an H or H2 buffer).