You definitley don't want to get into changing the gas tube just for the sake of installing quad handguards. Carolina Shooting Supply ( http://store.carolinashooterssupply.com/servlet/StoreFront ) sells a tri-rail and and seperate top rail to make the quad rail for the 308. Some people have also purchased the UTG quad rail for the .223/ 7.62x39 ( http://store.a51tactical.com/index.php?mai...roducts_id=2028 ) and installed it on their 308's after applying some dremel-ology to them.