This upper is light and ultra-fast. The low profile handguard covers a free-floating 13.5-in. barrel with Armalite’s own tunable muzzle brake. An adjustable gas block also allows the rifle to be individually set for optimal performance. An adjustable gas block also allows the upper to be individually set for optimal performance. Armalite AR-10 A-Series 13.5 Competition Complete Upper Half Assembly UAR103GN13