Short, carbon fiber, and 308 are all a little bit of contradictions. Like Husky said the weight difference is minimal on a short barrel. As far as CF goes a 308 seems like a good idea because of the long barrel life. But in my experience CF barrels don't really do that well as "beater" barrels. Like a lot of people use shorty 308's for. They are much better suited for super short round count range sessions like hunting barrels because of the mirage issue with them. Often times when I shoot some of my CF barrels I'm wondering if it's the mirage that's making POI shift or thermal shifting.