The M16A2 Buttstock is about five/eight" of the inch for a longer period then the sooner styles. Due to the greater duration it employed a longer buttstock screw and also a spacer. The swivel is mounted nearer towards the buttplate. This buttstock is at this time applied within the M16A4: https://gold-cup-trophy-colt-4568011.birderswiki.com/1037771/not_known_facts_about_colt_combat_unit_rail_gun_45