sentences:  The SIG MG 710-3 is an automatic, air-cooled belt-fed weapon operated by roller-delayed blowback and fires from an open bolt.The machine gun's bolt differs from other contemporary designs employing the roller-delayed blowback method of operation (such as CETME and Heckler & Koch designed weapons), being a 3-piece design that consists of a bolt head with two locking rollers, a striker sleeve and the bolt carrier which is connected telescopically with the bolt head.When a round is chambered pressure from the return spring drives the bolt and carrier assembly forward; simultaneously both rollers engage camming surfaces which drive the rollers outward from their compressed travel position into recesses in the barrel extension.