Ordnance Notes -- by Bob Stoner GMCM (SW) Ret.

ArmaLite/Colt Submachine Guns and Carbines

Introduction

Eugene Stoner, who was employed by ArmaLite Corporation in the 1950’s and 1960’s, developed the AR-10 rifle in 7.62 NATO caliber for the U.S. Army’s new NATO service rifle trials (about 1956). The AR-10 lost out, and Stoner used the design of the AR-10 to make a new, lighter, smaller caliber rifle called the AR-15. [AR stands for ArmaLite and the number stands for the design in the series.]

Chuck Dorchester, President of ArmaLite, went around marketing the new AR-15 to various military and law enforcement agencies. The Army tested early AR-15’s and rejected them. One of their points was the .223 Remington was not a standard U.S. military caliber.

General Curtis LeMay, who ran the USAF’s Strategic Air Command, was looking for a replacement for worn-out M1/M2 .30 Carbines issued to that branch. LeMay and Dorchester did some informal shooting of the new AR-15 over a weekend in the country. The upshot was that LeMay decided that the USAF had to have the AR-15 for his troops.

I won’t go into the convoluted history of the introduction of the AR-15, later M16-series into U.S. service. What I will do is discuss the development of various short rifles based on the AR-15/M16 design. Because ArmaLite did not have the production capacity to produce this design in large numbers, ArmaLite licensed mass production to Colt Firearms, Inc.

Submachine Gun and Carbine Development

The first attempt at a “sawed-off” version of the AR-15/M16 was a gun designed for Special Forces and vehicle crewmen.

The Colt Model 607 submachine gun (SMG) was a compact weapon. [In reality, the arm was not an SMG (as they fire pistol calibers), but a carbine firing an intermediate caliber cartridge. Nevertheless, Colt called their design a submachine gun.] Colt called this carbine/SMG the CAR-15 (Colt/ ArmaLite Rifle-15). The CAR-15 was made with a retractable butt stock. It had an overall length of 26 inches with butt collapsed. The retractable butt stock resembled a shortened standard rifle butt stock, but had a two-position latch recessed in the back that allowed it to be extended and locked into position. Length of pull increased by 2.7 inches.

A left side view of a Colt Model 607. This was the first attempt at a compact version of the M16 rifle. It used a telescoping butt stock, a 10-inch 1-in-12 twist barrel, a modified triangular handguard, and a 3.5-inch sound and flash moderator.

A right side view of a Colt Model 607 with its stock extended. Note the lower guide rod for the sliding stock. The latching lever is shown in the inset. This particular CAR-15 has a cut down pistol grip.

The CAR-15 barrel was too short to mount a bayonet, and so the SMG had no bayonet lug. Some 50 CAR-15 SMGs were made. Most were issued to Navy SEALs (about 1962) and Army Special Forces, though some were also given to Army K-9 units. The Model 607 never went into full production and these CAR-15 SMGs were assembled from available spare parts.

A close-up view of the Model 607 3.5-inch sound and flash moderator. The unit was designed to help tame the massive muzzle blast and flash generated by powder burning in a 10-inch barrel instead of the 20-inch barrel of the AR-15 or M16.

The Colt Model 608 CAR-15 Survival Rifle was meant for use by downed aircrew. Because of the CAR-15's modular design, the Survival Rifle could be broken down into two subassemblies and stowed with four 20-round magazines in a pilot's seat pack. With only a 10-inch long barrel, the assembled weapon was 29 inches in overall length. The Survival Rifle used a fixed tubular plastic-coated aluminum buttstock and a round handguard; neither were used on the other CAR-15 versions. The Model 608 did not have either a forward assist or a bayonet lug. The pistol grip was chopped down, and the muzzle was equipped with either a conical flash hider or the 3.5-inch sound and flash moderator of the Model 607.

The USAF had Colt develop the Model 608 for use by downed aircrews and pilots. The Model 608 had a fixed stock, shortened pistol grip, slim round handguard, and either a cone-shaped flash hider or the 3.5-inch sound and flash moderator of the Model 607. This specimen has an early waffle-stamped 20-round magazine.

A left side view of another Model 608 with the Model 607 3.5-inch sound and flash moderator. The USAF did not adopt the Model 608.

The characteristics of the Models 607 and 608 were combined into the Model 609 “Commando” version of the CAR-15. In 1966, Colt engineer Rob Roy designed a simpler two-position telescoping tubular aluminum buttstock to replace the stocks of the Models 607 and 608. The fragile triangular handguards were replaced by reinforced round handguards. Each half of the round handguard was identical, simplifying logistics. This new version of CAR-15 “Commando” was called the Model 609 (with forward assist) for the bolt and and the Model 610 (without forward assist) for the bolt. Both versions were equipped with a 4.5-inch sound and flash moderator instead of the three-prong standard flash suppressor of the M16/M16E1. The USAF classified the Model 610 as the XM177 or GAU-5/A submachine gun (GAU = Gun, Airborne, Unit – 5/A = aircraft equipment).

The Model 609 was type standardized as the XM177E1. This model has the redesigned telescoping stock, forward assist (same as the M16E1), round handuards, and the new 4.5-inch sound and flash moderator.

The Model 610 was type standardized as the XM177 (and GAU-5/A by the USAF). This model was the same as the Model 609 except it did not have the forward assist (the same as the M16). Barrel length of both XM177 and XM177E1 was 10-inches. Both XM177 and XM177E1 used the standard M16/M16E1 rifle handguard slip ring.

The Army purchased 2,815 Model 609 Commandos on June 28, 1966, and designated them the Submachine Gun, 5.56 mm, XM177E1. Most XM177E1’s were shipped with 20-round magazines because Colt was unable to build a reliable 30-round curved magazine that would fit in the M16 magazine well. The exception was 5th Special Forces Group that received a total of four early 30-round magazines. Colt completed delivery of the purchased XM177E1’s in March 1967.

1967 field tests led to Colt’s lengthening the Commando barrel from 10 inches to 11.5 inches. Muzzle blast and noise were reduced. The longer barrel also allowed fitting of the Colt XM148 grenade launcher. A metal bushing was added behind the sound and flash moderator to allow mounting of the XM148. The bushing also allowed firing of rifle grenades from those XM177E2 units without the XM148 launcher. Chambers of these XM177E2 rifles were chrome-plated. Commandos with the longer barrels were called the Model 629 or XM177E2 (with forward assist) and Model 649 or GAU-5A/A (without forward assist). In April 1967, the Army purchased 510 Colt 629 (XM177E2) Commandos for use by Military Assistance Command, Vietnam Studies and Observations Group (MACV-SOG). Delivery was completed by the end of September 1967.

The Model 629 was type classified as the XM177E2. This version introduced the 4.5-inch sound and flash suppressor with grenade launching bushing. The bushing helped guide the tail boom of the rifle grenade when it was fired. The bushing also located the front attachment lug of the XM148 grenade launcher. When the XM148 grenade launcher was used, the lower handguard was removed.

The Air Force adopted the Model 649 without the forward assist feature as the GAU-5A/A. The XM148 proved to be fragile and complicated to maintain in the field. It was replaced by Aircraft Armaments, Inc. (AAI) M203 design. The M203 replaced all XM148 units and it is still in service with American forces.

This XM177E2 has the Colt XM148 grenade launcher attached to the barrel. Note the removed lower handguard. The triangular-shaped rear handguard slip ring was introduced on this model. A triangular shape was used to help the soldier remove the handguards for maintenance. The trigger for the grenade launcher is the black, L-shaped handle attached to the firing rod. When the handle was up (below magazine release button, in photo) the launcher was on safe; when it was down, the launcher would fire. The small pistol grip had a lever to unlock and open the breech of the launcher for loading or extracting of grenades.

An XM177E2 equiped with the AAI-designed M203 grenade launcher. In this photo, the M203 is incorrectly mounted to the barrel – it is not seated against the barrel nut and the rear of the trigger guard is not latched against the lip of the magazine well. The leaf grenade sight is not attached to the handguard. To load or unload the launcher, the grenadier pushes the latch (directly below the sight base) and slides the barrel forward. A 40mm grenade round is then loaded (or fired case extracted before loading) and then the barrel is pulled back to latch. The safey (located to block the trigger) is set to OFF and the trigger pulled to fire the grenade.

Problems with range, accuracy, barrel fouling, and usage of tracer bullets plagued the XM177-series. Colt estimated that it would take a six-month $400,000 program to do a complete ballistic and kinematic study. Colt also recommended a 29-month $635,000 research and development program. Both recommendations were declined by the U.S. military as American ground force’s involvement in the Vietnam War was winding down. Production of all versions of the CAR-15 Commando ended in 1970.

A Navy SEAL shows off his XM177E2 with attached M203 grenade launcher.

After the Vietnam War, Colt abandoned the CAR-15 concept, but continued to develop heavy-barreled rifles, carbines for military use. These were marketed under the M16 or M16A1 name, while the civilian and law-enforcement semi-automatic counterparts were marketed as AR-15s.

In the early 1970s, Colt began development of an M16A1 carbine with a 14.5-inch long barrel. The 14.5-inch length was compatible with the existing carbine-length gas system and allowed for the mounting of a standard M16 bayonet. Despite having a longer barrel, it would not be less compact than the previous carbines. Only the Model 653 M16A1 carbine, with retractable buttstock and forward assist would be purchased in significant numbers by the U.S. military. The United States Army, Navy and Air Force, as well as the Malaysian Armed Forces, purchased Model 653s in small numbers for special operations forces or security forces.

The Colt Model 653 was based on the M16A1 rifle, but with a 14.5-inch barrel. The standard rifle flash suppressor was used. The round handguards introduced by the XM177-series were retained on this model.

During the Yom Kippur War, the American government sent arms and equipment, including Model 653s, to the Israeli Defense Forces. These Model 653s, called "CAR-15s" by its users, continue to be in use with the IDF today. Colt also licensed Elisco Tools to produce the M16A1 carbine in the Philippines as the Model 653P.

In the mid-1970s, the Bureau of Alcohol, Tobacco, and Firearms (BATF) declared the 4.25-inch long sound and flash moderator a sound suppressor (or silencer). During the Carter Administration, the U.S. State Department banned the sale of sound suppressors to foreign countries. Colt therefore designed carbines without the moderator.

The 4.5-inch sound and flash moderator used by the XM177-series. The two lower photos are sectioned to show the construction of the unit. Burning propellant was circulated between the inner and outer walls of the unit to cool it while the six oval slots acted to break up muzzle flash. To the shooter, the sound of the M177-series compared to the M16/M16A1 were roughly identical. BATF tests showed that the sound and flash moderator actually decreased the sound of the expanding gases by a few decibels. This was enough for them to classify the unit as a “silencer” and thus fall under the National Firearms Act of 1934.

In the early 1980s, at the request of the United States Marine Corps, Colt upgraded the M16A1 to the M16A2 rifle. Major changes were a reinforced lower receiver, a case deflector, a redesigned flash suppressor to double as both a suppressor and muzzle brake, and a 1-in-7 twist barrel. The 1-in-7 twist barrel was required by the switch from the 55 grain M193 bullet to the 62 grain M855 bullet. The M16A2 rifle's barrel was also thicker for the portion in front of the handguard. Colt incorporated these changes into its carbines, which it called the Model 723. As with the Model 653, the United States military made small purchases of the Model 723 for its special operation forces.

In 1983, Diemaco developed a carbine similar to the Model 723, call the C8 for use by the Canadian Forces. Original C8s were built by Colt as the Model 725.

In 1984, the United States government asked Colt to develop a carbine with maximum commonality with the issue M16A2. Colt named the carbine as the XM4. The M4 was adopted for United States service in 1994.

The M4 carbine has a detachable rear sight and carrying handle. This allows the fitting of various accessories such as the ACOG quick-reaction sight. The M4 has an improved telescoping butt stock over the XM177-series and Model 653. The handguards of the M4 and M4A1 are strengthened, and the barrel is cut to accept the M203 grenade launcher. The difference between the M4 and M4A1 is in the selector: the M4 is Safe, Semi-auto, and 3-round burst; the M4A1 is Safe, Semi-auto, and Full-auto.

The M4A1 carbine with M203 grenade launcher. The launcher is correctly mounted on the barrel. Compare how the back of the launcher trigger guard latches to the lip of the magazine well with the M203 mounted on the XM177E2 shown above. This M4A1 uses the Trijicon Advanced Combat Optical Gunsight (ACOG). It has the new RAS (rail accessory system) handguards with rails for the mounting of accessories. Rail covers are mounted on the top and sides to cover the sharp corners of the rails.

The United States Air Force made upgrades to its GAU-5/A and GAU-5A/A submachine guns to the GUU-5/P carbine. The barrels and moderators were replaced with the longer 14.5-inch barrel of the M4 (1-in-7 twist) or a complete upper receiver assembly replacement. Original GAU-5/A or GAU-5A/A markings were removed and the weapons restamped GUU-5/P. (GUU = Gun, Non-airborne, Unit – 5/P = personal equipment)

An Army soldier in Iraq talks on the radio. His rifle is an M4A1 carbine with an Aimpoint M68 reflex sight and AN/PEQ-2 laser designator.

A Navy Mk 18 Mod 0 modification of the M4A1. Note the very short 10.3-inch barrel and the new handguards with the rail covers installed. Removal of the carrying handle and rail covers allows mounting of various sighting devices, laser designators, handgrips, and other items by the individual soldier.

U.S. Navy SEAL Teams are using modified M4 carbines that use a 10.3-inch barrel. The modified M4’s are called the Mk 18 Mod 0.

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