Ordnance Notes -- by Bob Stoner GMCM (SW) Ret.
ArmaLite/Colt Submachine Guns and Carbines
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.
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.
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 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 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 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.
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.
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.
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.
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 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)
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.