The M16A2 Buttstock is about five/eight" of an inch longer then the earlier products. Due to elevated length it utilized a longer buttstock screw in addition to a spacer. The swivel is mounted closer to the buttplate. This buttstock is now used on the M16A4: The modification procedure described below https://simonabyvu.magicianwiki.com/973759/the_5_second_trick_for_colt_combat_elite_commander_45_acp