The M16A2 buttstock is about five/8" of an inch for a longer time then the earlier versions. Due to the increased length it employed a longer buttstock screw in addition to a spacer. The swivel is mounted nearer for the buttplate. This buttstock is at present used within the M16A4: https://devinhjifb.wikinewspaper.com/3397186/the_basic_principles_of_colt_combat_unit_rail_gun_45