Custom Products Combat Classic .693 20" Barrel Autococker Pants & Slide Shorts • POSITIVE FEED LIVE HINGE 4v Small Buffer Tube • POSITIVE FEED LIVE HINGE TRAY While existing designs may require a low force to open the exhaust valve they are still bound by the need to overcome blowback using the speed and mass of the bolt which means that the valve has to be opened with a greater speed than is actually required The entire barrel has been "fluted" and has superior porting to reduce noise and improve accuracy The Combat Classic Barrel is machined and honed to the same exacting standards as the Combat Pro System but does not have the interchangeable tip or optional hand guard thread adapter