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Colt's AR-15 Model 601 Automatic Rifle

Before the M16 existed, the Colt AR-15 Model 601 was in combat in Vietnam!

Colt's AR-15 Model 601 Automatic Rifle

The Colt AR-15 Model 601 played an important role in military history eventually evolving into the M16 series. Today it is a popular model to clone among “retro” builders. (Michelle Hamilton photo)

In the summer of 1959, Colt Manufacturing procured the rights and patents to a rifle destined to not only revolutionize the military small arms of the United States and NATO forces, but would also become the most popular civilian Sporting Rifle of all time, the AR-15. It began its life as a prototype with the Armalite Company, a Hollywood, California-based Research and Development division of the Fairchild-Hiller Corporation. It was designed by Armalite Engineers Bob Fremont and L. James Sullivan. Many redesigns and rolling changes would take place from 1957 to 1959 on Armalite’s prototype AR-15 rifles, leading to the finalization and design Colt would ultimately begin producing.

In 1959, Armalite Corporation sold the patents of the AR-15 rifle and corresponding gas system to Colt Mfg. for a sum of $75,000 plus royalties on the first production rifles. The procurement was arranged by the Baltimore Maryland law firm, Cooper-McDonald Company. In December of 1959, Colt would begin producing a variant of Armalite’s rifle and designated it the Colt AR-15 Model 601. This .223 Caliber Automatic Rifle would feature a unique 1 turn in 14 inches rifling twist, “pencil weight” barrel and fed from a 20-round detachable box magazine. It is believed the 1-14 inch barrel twist was a design “left-over” from the .222 Remington, an early AR-15 chambering from Armalite’s prototype rifles.

Colt AR-15 Model 601 Automatic Rifle
The Colt AR-15 Model 601 was developed for military sales and would go on to see combat in Vietnam with both US and ARVN troops.

In February 17, 1960, the Cooper-McDonald Co. of Baltimore Maryland would acquire a single rifle from Colt Mfg. This early Model 601 (Serial number 106) would become one of the most historically significant small-frame ARs in existence. On 4 July 1960 serial number 106 would be introduced to Vice Chief of Staff to the United States Air Force, General Curtis LeMay. At this time, LeMay was attending a barbeque at Richard “Dick” Boutelle’s Maryland farm. Dick Boutelle was the CEO of the Fairchild-Hiller Corp., whom had a vested interest in the U.S. Department of Defense procuring this new lightweight .22-caliber Assault Rifle. Presented to Curtis LeMay was serial number 106, more commonly known today as the “coconut rifle”. Serial number 106 was the 6th production rifle from Colt, placing production in early December 1959. The rifle gained its name through field tests in foreign countries, which often used coconuts as physical targets.

Curtis LeMay was quite impressed with the lightweight, easy to maneuver rifle. He was allowed to fire number 106 at varying ranges, using watermelons as the targets. These blew up in spectacular fashion. Easily and effortlessly dispatching three of the four watermelons, LeMay made up his mind. He had to have this new “wonder rifle” to replace the aging M1 and M2 Carbines then fielded by U.S. Air Force Security Forces (U.S.A.F. Military Police) guarding Air Force bases. After LeMay and company “ate the son of a bitch” (speaking of the last remaining watermelon) he would verbally place an order for 80,000 rifles with Colt. Ultimately, the U.S. Air Force would be supplied with between 8,000 to 8,500 total model 601 rifles, with the first contract shipment reaching Air Force hands in May of 1961. This began the (now) 60 years of military service for the AR-15/M16 rifle.

Colt AR-15 Model 601 Automatic Rifle
The Model 601 has a number of small subtle differences compared to the later M16A1. These include the charging handle, lack of a forward assist, unshrouded mag release, no rear sight markings on receiver and the non-captive pivot pin to name a few. (David Fortier photo)

Several official evaluations were made of the AR-15 Model 601, including at the U.S. Air Force Marksmanship School, Lackland AFB, on September 22, 1960. There is also a report number DPS-96, “Test of rifle, Caliber .223 AR-15” dated 9 January 1961 from the Aberdeen Proving Ground in Maryland. Our main focus, however, will be the Advanced Research Projects Agency (ARPA, now DARPA) study of the Model 601 in combat. Based on observations found by both U.S. Military Advisors and RVNAF Commanders, using the AR-15 in limited live fire demonstrations during the month of August 1961, 601 rifles would be requested in larger numbers. Sufficient numbers were requested for a full-scale combat evaluation of this light automatic rifle. In December of 1961, Secretary of Defense Robert McNamara approved the procurement and shipment of 1,000 AR-15 601 rifles, along with necessary ammunition, parts and accessories for field evaluation.

Contracts between the Office of Secretary of Defense (OSD)/ARPA and Colt Mfg. were negotiated and fulfilled through the Cooper-McDonald firm of Maryland. Within roughly a month (January 27, 1962) the first air shipment of AR-15s were in the field. They would continue arriving every three weeks until the fulfillment of the contract on 15 May 1962. Combat Operations and full evaluation of these 1,000 rifles began on 1 February 1962 and would end on 15 July 1962. This near 6 month trial of the 601 would be known as ARPA’s Project AGILE. The rifle received glowing reports by both U.S. Air Force personnel and U.S. Special Operations Forces deployed in Vietnam during this time. They found that this lightweight selective-fire small-caliber rifle not only met, but exceeded the performance of the standard-issue 7.62mm M14 service rifle. The performance curve also vastly exceeded aging military small arms, ultimately leftover from World War II and Korea.

Colt AR-15 Model 601 Automatic Rifle
The early charging handle was triangular in shape and harder to manipulate than the later design. Also, note the rear sight markings are on the sight and not forged into the upper receiver. (David Fortier photo)

Between December 1959 and 1963, a total of 14,500 AR-15 Model 601 rifles would be produced. Many of these rifles would be procured by the U.S. Air Force and OSD/ARPA. Remaining rifles would ultimately find their way to places such as the Pasadena Sheriff’s Department, other Police Agencies, Government Agencies and the Commercial market. Roughly 100-300 rifles would be acquired by the U.S. Navy SEALs and foreign militaries including: Australia, Burma, India, Singapore and Malaya. The first 100 rifles (serial number ranges 101-200) would feature non-painted, bakelite furniture (much like the coconut rifle), giving the furniture almost a “burled” appearance. From this point forward, however, the stocks would be painted a green finish (serial number ranges 200-14,484).

Numerous components of the Colt 601 (and into the transitional 602) were unique and still bordering on the “prototype” status. The 1x14 rifling twist pencil weight barrel for instance, featured a leftover twist rate from the Armalite prototypes. Many of the initial barrels for the 601 were produced by Winchester for Colt Mfg., and featured Winchester proof marks under the cast front sight base. The “duckbill” style three-prong flash suppressor was unique to the 601. It gained its nickname through the thinner, almost lip-like appearance. The upper receiver featured no windage adjustments forged into the upper receiver, all markings were found on the windage wheel (which was simply an arrow and R). Another “leftover”, this one from serial number 4 of the Armalite AR-15, was the triangular charging handle. This charging handle, while in the traditional location, was hard to grasp (especially with gloved hands) and quickly changed on post-1963 Colt rifles (see Colt AR-15 Model 602).

Colt AR-15 Model 601 Automatic Rifle
The 601’s pivot pin was not captured, plus the gas tube was not manufactured from stainless steel. (David Fortier photo)

Differences between the 601 compared to the M16A1 and even 603/XM16E1 are numerous. The non-captive pivot pin slabside lower receiver featured no magazine release fencing. Type A and B stocks, with solid rubber buttplates, early designed “Edgewater” buffers, “divot” lower parts and controls which include; rear takedown pin, selector, trigger pins, pivot pin. Chrome bolt and carrier, with early designed solid hammer pin. Cast front sight base, non-stainless steel gas tube and early “Colt/Armalite” and “Patent Pending” roll marks on the lower receiver.

While the Air Force Security Forces Model 601s largely sat in racks hoping Soviet Spetsnaz never kicked in their door, the Navy SEALs, Army Special Forces and ARVN troops put their 601s to good use. Why was the 601 successful? While an imperfect design in the end, it brought a number of positive attributes to the table. For the already over-burdened soldier, both it and its ammunition were significantly lighter than an M14 or Thompson submachine gun. Compared to .30 carbine, .223 ammunition was also significantly lighter, flatter shooter with improved terminal performance. The rifle was very accurate and easy to hit with at the typical combat distances encountered in Vietnam. On full automatic it was fairly easy to control with a higher hit probability than its peers. Plus, the controls were well laid out and easy to manipulate. All of these features improved the individual soldier’s survivability on the modern battlefield.


Colt AR-15 Model 601 Automatic Rifle
The 601 featured a pencil weight barrel with an odd 1x14 inch rifling twist which performed well in Vietnam, but poorly in cold weather testing leading it to be changed to 1x12 on later models. Also note the design of open flash suppressor. (David Fortier photo)

Even with all its positive attributes though, the 601 did have issues. The pivot pin was not retained and could be lost. The magazine could be accidentally ejected due to the lack of a shroud around the mag release. The charging handle was poorly designed. The buffer needed improvement. The barrels and chambers rusted easily. Magazine capacity was insufficient for use in conjunction with fully automatic fire. Troops had a habit of breaking open C-ration bands (it was the perfect size and shape) with the flash suppressor, breaking it. Accuracy past 300 yards was inferior to the 7.62mm M14. There were other issues, but you get the point. The 601 was a good effort which fell short. It did however point the way to the future, ultimately the M16A1.

Colt AR-15 Model 601 Automatic Rifle
The AR-15 Model 601 performed well during field trials in combat during the war in Vietnam ultimately leading to improvements and eventually the M16A1.

The Colt Mfg. AR-15 Model 601 Automatic Rifle remains a historically significant and pivotal rifle in the history of the “black rifle”. Through field testing, determination, trial and error, the 601 paved the way for the M16 rifle, M4 Carbine, AR-15 Sporter and AR pattern rifles. Becoming a military favorite, to a mechanical failure, to a logistical nightmare and back to a military (and civilian) favorite the 601retains its love from historians, firearms enthusiasts, experts and an unfound gem for those seeking to gain information on the history of the “Sweet 16”.

If you have any thoughts or comments on this article, we’d love to hear them. Email us at

About the Author:

Michelle Hamilton has a Bachelor’s degree in Criminal Justice/Homeland Security, is a serious student of military history, small arms design and manufacturing and is a competitive shooter.

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