The M16A2 buttstock is about five/8" of the inch longer then the sooner designs. Because of the improved size it used a longer buttstock screw and also a spacer. The swivel is mounted closer to your buttplate. This buttstock is currently utilised on the M16A4: Up for sale is often https://coltm16a1forsale36977.ambien-blog.com/37511262/facts-about-colt-combat-unit-rail-gun-45-revealed