Several Rifles ended up rebuilt, Particularly Vietnam era rifles. Usually the barrels had been changed. Some examples of markings found on replacment barrels contain: It has the early reciever without any fence round the mag release and all early form launch pins with holes in the middle. If you prefer https://kylernomje.wikiadvocate.com/6399201/not_known_facts_about_colt_combat_unit_rail_gun_45