I have an AR with a Proof Research Carbon fiber wrapped barrel. It does save weight but the savings is relative to the contour and length of your barrel.
Expect a 40% weight savings relative to a barrel of the same length and contour.
A trusted industry insider I know (but whose name I won't use here) has been to Proof Research and shot their stuff. He came away thoroughly impressed.
Christensen Arms makes an AR with a wrapped barrel, not sure if they offer just a barrel though. Have seen one of bolt rifles at a range once and it was pretty impressive.