Very nice AR15 A2. Colt finally came out with the A2 when they ran out of A1 parts for their earlier AR15 series. Colt has a history of never throwing out good parts when they can be sold to the public. During the M16icon production if the government required changes to the M16 series. Those parts no longer accepted by the government would be transferred to the civilian production. That's is why you see a progression of differences in the civilian AR15 from early flash hiders, Buttstocks without trapdoors, etc. A prime example is on your rifle. Please note the lower receiver is an early slab sided flat type without the fence around magazine release. The lower receiver was made from the large amount of forgings that were purchased for the early M16 rifles. When the government very quickly went to the partial and then full fence lowers these flat sided forgings were unusable for the military contracts, those were used in the civilian AR15 production. They had so many that these slab sided lower forgings were used into the 1980's.