Caliber: 5.56 NATO. Barrel: 16.1″ chrome-lined. Sights: Adjustable. Based on military M4. Direct gas/locking bolt operating system. Magpul MOE handguard, carbine stock, pistol grip, vertical grip. Magpul SL Black version has black Magpul MOE SL handguard, buttstock, pistol grip, and vertical grip, and A2 front sight and flat-top upper receiver. FBP includes Geissele 13” MK4 rail system and Magpul Pro flip-up front and rear sights. Colt OEM Series omit handguards, buttstock, triggerguard, magazine, and rear sight. OEM1 accepts most aftermarket drop-in style handguards that utilize the factory barrel nut and retaining ring. Also available with low profile gas block and without handguard retaining ring. OEM2 has low-profile gas block and without handguard retaining ring to fit aftermarket free-float handguards. Values are for the CR6920 model. Add 13% for the M4 Carbine Magpul SL Black variant; add 44% for the M4 Carbine FBP variant; and subtract 22% for the M4 Carbine OEM1 and M4 Carbine OEM2 variants.