All in all, for the civilian market the civilian model MSR (AKA ‘AR-15’) in any form variation never originated as a military only rifle.

Briefly; It all originated with a civilian market rifle Armalite wanted to develop to capture a growing market niche of consumers who wanted a semi-auto rifle with military ‘cosmetics’ styling for a ‘sporting’ type of rifle. So Jim Sullivan and Robert Fremont went to work on design of a civilian market rifle that carried forth the military type of ‘cosmetics’ theme of the AR-10, Stoner joined in. This civilian only rifle was designated AR-15 as it was the 15th rifle in the Armalite design series. While developing the civilian only model Stoner started talking Armalite into trying to capture the military market, his real interest was in military firearms, and took the civilian design designated AR-15 and made changes, and development of the origin civilian model stopped. But the Stoner design still carried the AR-15 designation as it wasn’t a new rifle in the design series but basically just an adaptation to change directions with the design towards a military rifle and eventually he gets the credit for ‘creating the AR-15’ (because what he did design was the AR-15 but only because it carried forth the origin civilian rifle designation) and it gets tagged as a military rifle.

The origin of the M16/M16E1/M16A1/M16A2/M4, the XM177 & GAU-5, and all other variations literally originated from a civilian only rifle design and its origin was never as an ‘assault rifle’ or ‘weapon of war’, its origin was as a civilian market semi-auto sporting rifle with military styling ‘cosmetics’.

Clarification for: “The other CAR-15 series went on to become the M16/M16E1/M16A1/M16A2/M4. (From the M16A2 came variations that eventually led to the M4).

Colt had made a carbine model of the M16A2, it was the Model 723 and was purchased for use by special operations groups. Then a Canadian company Diemaco, under license from Colt, developed the C8 carbine for Canadian Forces and it was based on and similar to the the Colt Model 723. But the first runs of the C8 were built directly by Colt as the Model 725. In 1984, the U.S. asked Colt to develop a carbine with maximum commonality with the issue M16A2. Colt created a carbine called the XM4 that was based on the Model 723 but also had some C8 variation. That project eventually resulted in the development of the M4 carbine.

The other CAR-15 series went on to become the M16/M16E1/M16A1/M16A2/M4. (From the M16A2 came variations that eventually led to the M4).

The ‘CAR’ in ‘CAR-15’ didn’t actually stand for ‘carbine’ in the development programs – it was the internal Colt designation for ‘Colt Armalite Rifle’.

The Colt CAR-15 series (that became the XM177 & GAU-5 eventually) really started in 1964 with the SMG Model 607 they sent to the Army for testing. Then in 1966 Colt came out with the XM177 & GAU-5 series which was an out growth of the Model 607. There were five different variation models in service.