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The Colt AR-15 Transitional Model 01:The Missing Link

By William D. Ehringer

The AR-15 series of rifles, invented by Eugene Stoner, has become the standard by which many modern small arms are judged. The first AR-15 rifles, which were manufactured by Armalite and marked, “Armalite AR-15 Costa Mesa Calif. USA”, were a radical departure from the small arms developed up to that date. The use of aluminum and plastic composites made the gun lightweight, which also made the gun attractive to military small arms analysts and end users. However, the AR-15 incorporated a number of not so novel ideas in its construction. For example, the hinged upper and lower receiver is very similar to the FN FAL, the dust port cover similar to the MP-44 and the bolt design was also similar to the Johnson semi-auto rifle. Considering the fact that the AR-15 incorporated the best design features of so many great machine guns as well as the new design features Eugene Stoner was responsible for, the gun still had many problems. The goal of this brief article is to introduce an AR-15 variant which attempted to address the many design flaws of the early AR-15 Model 01. This AR-15 variant could be argued as the missing link between the Model 01 and the M16 rifle that became the standard issue weapon for the U.S. armed forces in the late 1960s.

In December of 1959, Colt Manufacturing Company acquired the manufacturing rights to the AR-15 from Armalite. The adoption of the AR-15 met stiff opposition, especially from the Army Ordnance staff. However, after several cunning business moves on the part of Colt, Secretary of Defense McNamara ordered over 100,000 AR-15 rifles for issue to troops in Vietnam. The military was less than enthusiastic about the AR-15 Model 01 (correctly known as the Model 601). A number of serious issues were raised about the Model 01 and included the following: the gun fouled easily (which was traced to the powder being used and lack of adequate cleaning kits), the gun when fouled would not go into battery very easily, the duckbill flash hider got easily tangled in weeds or brush, the magazine release was unprotected and could accidentally be engaged if the gun was laid on its right side, the small charging handle was not ergonomically designed and hard to manipulate, the barrel and chamber were made of steel and rusted easily, the sling swivel was not fixed and rattled against the plastic stock, and the high cyclic rate of the gun coupled to its 20 round magazine left soldiers with an inability to adequately deliver controlled full-auto fire.

The Colt/Armalite AR-15 Model 01 was destined to be a failure unless the design flaws of the Model 01 were addressed. Shortly after Colt had acquired the manufacturing rights to the AR-15 from Armalite, Colt then bought the patent rights to the AR-15 from Armalite and started manufacturing a new exclusively Colt designed AR-15. However, the very first AR-15 rifles manufactured and produced solely by Colt were not marked Model 02 as is often quoted in many books and articles on the evolution of the AR-15. The fact is, Colt exclusively manufactured an AR-15 Model 01 which is also known as the “AR-15 Model 01” transitional gun (Figure 1).

The Model 01 transitional gun encountered by this author had a number of “blended” features which undoubtedly make this AR-15 very different in some aspects from the M16 (Figure 2), but at the same time the two rifles share in common some unique features. For example, the Model 01 transitional gun still retains the original and obsolete Model 01 buffer (Figure 3A). This extremely lightweight buffer resulted in the high cyclic rate of the early AR-15s and was also the source of many failures associated with the weapons full-auto mode. In contrast the M16 buffer (Figure 3B) was considerably heavier and had individual weights inside of the buffer body that reduced the bolt bounce problems associated with the AR-15 Model 01.

The buttstock of the Model 01 (Figures 4 and 5) transitional gun retained many of the inherent design flaws of the original Model 01. This included a sling strap swivel that moved, narrow buttplate, and lack of a trapdoor for the cleaning kit. The overall length of the AR-15 Model 01 buttstock was about 1” shorter than the M16. The AR-15 Model 01 transitional gun buttstock was composed of a plastic composite versus the considerably stronger fiberglass reinforced M16 buttstock. However, the Model 01 transitional guns stock was black, which is quite different from the original Model 01’s green or black painted over simulated wood finish. Also evident in this photograph is the improved charging handle with its wider finger grooves. The same type of charging handle is also typically encountered on the M16.

The early duckbill flash hider typically encountered on the Model 01 had a bad habit of bending or breaking, and thus Colt manufactured a different flash hider called the three-prong flash hider that was noticeably stronger than the original duckbill flash hider. The Model 01 transitional gun has a three-prong flash hider (Figure 6) that is identical to the one found on later M16 rifles.

The bolt carrier of the Model 01 transitional gun is a hybridized mix of the original model 01 features and later M16 features (Figure 7). The Colt/Armalite Model 01 had a chrome carrier (Figure 7C). One problem with the chrome carrier was that its surface was reflective, which gave away troop positions. The bolt carrier encountered in the transitional Model 01 (Figure 7B) was dull parkerized with a chrome carrier key. The opinion of this author is that the idea was to remove the flashy chrome of the carrier but retain the anti-rust properties of chrome where the gas impinged on the carrier. Furthermore, the Model 01 transitional gun bolt carrier lacks the forward assist notches and the upper receiver (not shown) also lacked the forward assist.

The thought that this Model 01 was potentially a “one-off” or a “parts gun” was seriously contemplated. The author contacted Dennis Todd, a well-known Class III dealer who specializes in Colt M16-type rifles. Mr. Todd has consistently stated that the term “never” and “always” should not be used when describing many military weapons. Mr. Todd had the following comments regarding Colt manufactured M16 variants. “A common manufacturing process is to improve upon the design of a particular weapon during a production run. Defense contractors are constantly product-improving their items as a result of internal R&D, governmental R&D, and field experience from end users. This is particularly true when a new design is first used in combat. Parts are manufactured or obtained from subcontractors as part of the continuous flow of materiel. When improved components are accepted by the military, there may be a supply of “obsolete” parts on hand. Sometimes the contract allows those parts to used until expended. Other times, the new parts are introduced immediately and the older parts become excess. Colt, and other contractors who manufacture products for export and the civilian/law enforcement market as well as for the US military have a place to use the obsolete items (assuming that they are not dangerously defective). Many export or civilian/law enforcement M16s and even AR-15s will have parts originally intended for US military rifles but that became obsolete or excess to military production.

The result is that the vast majority of rifles will be “textbook” correct, but a number, frequently at the start or end of a type run will be “unusual” but factory correct nonetheless.” Mr. Todd indicated that he had encountered, albeit limited numbers, AR-15 Model 01s in a similar configuration. The original paperwork was retrieved for the AR-15 Model 01 described in this article and it shows the gun being sold directly from Colt to a police department located in Illinois. Kiesler’s Firearms and Accessories purchased the gun directly from this police department, and the gun shows little or no use.

However, it is important to note that because of the mixing of components by Colt on the M16-variants, and the potential for transferred guns to have features changed, caution should be taken when assuming a certain M16-variant will have certain features. Clearly though the Colt AR-15 Model 01 serves as an important link in the evolution of the M16 rifle.


Special thanks to Martha Brown of Kiesler’s Firearms and Accessories and Dennis Royzer.


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