The Mod 2 fits on Mil-Spec carbine receiver extensions and optimized for intermediate length receiver extensions (MK2 AR10 A5). These improved lines also enhance shooting in the prone position while remaining snag free with no edges to catch or tangle in slings antenna or other PPE. Includes: BCM Stock Mod 2 – Black/BCM MK2 Receiver Extension (approximately 3/4 longer than carbine) 7076T6 8 position Mil-Spec diameter/Mil-Spec M16A4 Rifle Action Spring/BCM MK2 Mod 1 – T0 Buffer (weight = approximately 3.8oz)/BCM EPM4 End Plate (include mount for QD swivel)/Locking Nut (Castle Nut) M4