CAR - 15 The Colt Automatic Rifle - 15 Military Weapons System or CAR - 15 was a family of AR - 15 and M16 rifle – based firearms marketed by Colt in the late 1960s and early 1970s . Due to their compact size , the short - barreled Colt Commando and XM177 versions of this family continued to be issued to the U . S . military after the Vietnam War . The CAR - 15 name was an attempt to re - associate the AR - 15 name with Colt , since the AR initially stood for ArmaLite Rifle , the original manufacturer . Colt later abandoned the CAR - 15 concept , but continued to make variations , using the M16 brand for military - oriented models and the Colt AR - 15 brand for law enforcement and civilian models . However , in present usage , CAR - 15 is used as a generic name for carbine - length M16 and AR - 15 variants from before the M4 . Specifically , " Colt Commando " currently refers to the ultrashort 11 . 5 - inch barrel assault rifle of the Model 733 series . By comparison , the M4 Carbine has a 14 . 5 - inch barrel , while the M16 assault rifle series has a 20 - inch barrel . History . Starting in 1965 , Colt attempted to market the M16 rifle as a modular weapons platform that could fulfill all of the various needs of an army , similar to the marketing plans for the AR - 10 , its predecessor , and the Stoner 63 , its rival . In order to compete with the Stoner 63 which could be converted into a belt - fed light or medium machine gun , Colt also included the short - lived CMG - 1 and CMG - 2 machine guns in the CAR - 15 Military Weapons System , though the CMG - 1 and CMG - 2 had few parts in common with the CAR - 15s . By using various upper assemblies , buttstock s , and pistol grip s , the weapon could be configured as an assault rifle , a heavy - barreled automatic rifle , a carbine , a submachine gun , or as a survival rifle . Each variation had a Colt model number , meant for internal identification usage . The members of the CAR - 15 family , with the exception of the Rifle and Commando , only existed as toolroom prototypes and never entered full - scale production . As a result , wide variation due to experimentation exists within each model . The U . S . military only made significant purchases of the Rifle and Commando versions , so Colt abandoned the CAR - 15 family concept . The CAR - 15 Rifle was already identified by most users as M16s or AR - 15s , and the CAR - 15 name was similarly associated with the short - barreled Submachine Gun and Commando models . Because of that , the term " CAR - 15 " has been used to describe any M16 - based carbine , even if the particular weapon is not officially named thus . CAR - 15 Military Weapons System . CAR - 15 Rifle . The " Model 603 " CAR - 15 Rifle , adopted initially by the United States Army as the XM16E1 and then later as the M16A1 , and the " Model 604 " CAR - 15 Rifle , adopted by the United States Air Force as the M16 , formed the core of the CAR - 15 family . However , the United States military had already committed to purchases before Colt created the concept of the CAR - 15 weapons system . The principal difference between the Model 603 and Model 604 is that the former has a forward assist , allowing a user to manually close a stuck bolt . CAR - 15 Carbine . The " Model 605A " CAR - 15 Carbine was a shortened version for situations where longer weapons could be unwieldy , such as aboard vehicles or helicopter s . The only significant change from the M16 rifle was that the barrel was shortened to 15 inches in length , so that it ended just forward of the front sight base . Because of the shorter barrel , no bayonet mounting lugs were provided . One prototype used a shorter handguard and a 16 - inch long barrel . The " Model 605B " had no forward assist , but had a four - position selector switch ( developed by Foster Sturtevant in December 1966 ) so that a user could select safe , semi - automatic , three - round burst , or full automatic modes of fire . Unlike the standard three - position group , the four - position group went from ( going clockwise from the 9 o ' clock position ) safe , fully automatic , semi - automatic and finally burst . The selector itself had 360 degrees of motion , and could be moved either clockwise or counterclockwise , unlike with standard groups . Instead of three - round burst , the burst cam could be modified to two - round or six - round burst . Both versions used the rifle - length buttstock . As early as 1962 , United States Navy SEALs were using the CAR - 15 Carbine . CAR - 15 Heavy Assault Rifle . The " Model 606 " CAR - 15 Heavy Assault Rifles used heavy barrels ( HBAR ) for sustained automatic fire . Like the Browning Automatic Rifle ( BAR ) , the CAR - 15 HBARs did not have a quick - change barrel . The HBARs could be fitted with either a Colt bipod , a M14 rifle M2 bipod , or a modified BAR bipod . CAR - 15 Heavy Assault Rifle M1 . The CAR - 15 Heavy Assault Rifle M1 used 20 - round M16 box magazine s , which limited its ability to provide sustained rates of automatic fire . The 30 - round M16 box magazine was not available until 1969 . The " Model 606A " had a forward assist . The " Model 606B " had a forward assist and the four - position selector . The Army purchased fewer than 200 Heavy Assault Rifle M1s for use in the Small Arms Weapons Systems ( SAWS ) tests in 1965 . CAR - 15 Heavy Assault Rifle M2 . The CAR - 15 Heavy Assault Rifle M2 was a belt - fed version using heavily modified upper and lower receivers . Colt engineer Rob Roy designed a special ammunition box to hold a 50 - round or 120 - round ammunition belt as well as the expended links . The belt - fed CAR - 15 was similar to the belt - fed AR - 10 developed by Eugene Stoner and John Peck at ArmaLite . The Army evaluated its use as a helicopter door machine gun but rejected it , so less than 20 of the Heavy Assault Rifle M2s were made . CAR - 15 Submachine Gun . The " Model 607 " CAR - 15 Submachine Gun ( SMG ) was a compact weapon for use by special forces and vehicle crewmen . The dictionary definition of submachine gun is an automatic firearm that fires pistol - caliber cartridges . However , manufacturers such as Colt , Heckler & Koch , and Zastava Arms have referred to compact carbines as submachine guns , to emphasize their short length and to differentiate them from longer carbines . The CAR - 15 SMG was the first AR - 15 made with a retractable buttstock , with its overall length being only 26 inches with the buttstock retracted . The retractable buttstock resembled a shortened version of the fixed buttstock , but a two - position latch recessed in the back allowed it to be extended and locked into position , increasing the length of pull by 2 . 7 inches . The barrel is too short to mount a bayonet , so the SMG had no bayonet lug . About 50 CAR - 15 SMGs were made . Most were issued to Navy SEALs and Army Special Forces , though some were also given to Army K - 9 units . Since it never went into full production , CAR - 15 SMGs were assembled from available spare parts . The first models were made with M16 receivers without forward assists and with shortened pistol grips from the Survival Rifle ( see below ) . The later " Model 607A " was made with XM16E1 receiver with forward assist and standard pistol grip . The handguard was made from full - length rifle handguard by cutting it in half and using either the fore or aft pair , after machining the ends to fit the slip ring and handguard cap . Because of the short barrel , the CAR - 15 SMGs suffered from a loud and bright muzzle blast , and a number of muzzle devices were developed to reduce this . The SMGs were initially fitted with the standard M16 rifle ' s " duckbill " or three - prong flash hiders , which did not alleviate the problem . In September 1966 , Colt developed a 3 . 5 - inch long moderator that lessened the noise and muzzle flash , which also increased the weapon ' s reliability by increasing the amount of back pressure . However , the moderator created its own problems , such as heavy bore fouling and causing tracer bullets to wildly yaw . A 4 . 25 - inch long moderator with six slots and an expansion chamber , which further reduced noise and flash , replaced the previous muzzle device and became standard for the SMG and the Commando series , but fouling and tracer problems persisted . CAR - 15 Survival Rifle . The " 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 that were not used on the other CAR - 15 versions , and 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 long moderator . CAR - 15 Commando ( XM177 / GAU - 5 series ) . The CAR - 15 Commando was not initially part of the CAR - 15 Military Weapons System , but was added in 1966 in response to the US military ' s desire for a shorter M16 and the Model 607 SMG ' s inadequacies . Colt engineer Rob Roy designed a simpler two - position telescoping tubular aluminum buttstock to replace the complicated extending triangular version . The fragile and ad hoc triangular handguards were replaced by reinforced round handguards . Each half of the round handguard was identical , simplifying logistics by not requiring a top / bottom or left / right pair . The " Model 609 " Commando had a forward assist , while the " Model 610 " Commando did not . A " Model 610B " with a four - position selector was available , but not used by the U . S . military . All versions were equipped with the 4 . 25 - inch long moderator . The XM177 used a unique flash suppressor sometimes called a flash or sound moderator for its 10 inch barrel . This device is 4 . 2 inches long and was designed primarily as a counterbalance measure as the shorter barrel made the weapon unwieldy . This device reduced flash signature greatly and sound signature slightly , making the normally louder short barreled rifle sound like a longer barreled M16A1 . Although it has no internal baffles and does not completely reduce the sound signature to subsonic levels , because it alters the sound level of the weapon , the US Bureau of Alcohol Tobacco Firearms and Explosives has declared this muzzle device to be a sound suppressor and regulates its civilian purchase in the United States . The Model 610 was classified as the " XM177 " but adopted by the Air Force as the " GAU - 5 / A " Submachine Gun ( GAU = Gun , Aircraft , Unit ) . The Army purchased 2 , 815 Model 609 CAR - 15 Commandos on June 28 , 1966 , which were officially designated Submachine Gun , 5 . 56 mm , " XM177E1 " . As part of the contract , Colt was supposed to supply each XM177E1s with seven 30 - round magazines , but Colt was unable to build a reliable 30 - round curved magazine that would fit in the M16 magwell , so most XM177E1s were shipped with 20 - round magazines . The exception was 5th Special Forces Group , who received a total of four early 30 - round magazines . Colt completed delivery of the purchased XM177E1s in March 1967 . In 1967 , in response to field testing , Colt lengthened the Commando ' s barrel from 10 inches to 11 . 5 inches . The increased length reduced noise and muzzle flash , and allowed fitting of the Colt XM148 grenade launcher . A metal boss was added to the moderator for mounting of the XM148 and rifle grenade s . The chambers were chrome - plated . The Commandos with the longer barrels were called the " Model 629 " and " Model 649 " . The Model 629 Commando had a forward assist ; the Model 649 Commando did not . In April 1967 , the Army purchased 510 Colt 629 Commandos for use by troops assigned to the Military Assistance Command , Vietnam Studies and Observations Group ( MACV - SOG ) , and designated them " XM177E2 " . Delivery was completed by the end of September 1967 . The Air Force adopted a similar model without the forward assist feature as the " GAU - 5A / A " . Sources debate whether or not this was a Colt Model 630 or 649 . According to John Plaster and other sources , the lack of 30 round magazines continued to be problematic and SOG operators resorted to pooling their personal resources and purchasing the larger capacity magazines on the civilian U . S . market . Problems with range , accuracy , barrel fouling , and usage of tracer bullets continued to plague the XM177 series , but Colt estimated that it would take a six - month $ 400 , 000 program to do a complete ballistic and kinematic study . There were also recommendations for a 29 - month $ 635 , 000 research and development program . Both recommendations were declined by the U . S . military as American ground force involvement in the Vietnam War was gradually winding down . Production of the CAR - 15 Commando ended in 1970 . Post - Vietnam . After the Vietnam War , Colt abandoned the CAR - 15 Military Weapons System concept , but continued to develop heavy - barreled rifles , carbines , and Commandos 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 mid - 1970s , the Bureau of Alcohol , Tobacco , and Firearms ( BATF ) declared the 4 . 25 - inch long moderator a sound suppressor . 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 Car - 15 Colt Commando was used in the Salvadoran civil war and Guatemalan Civil War and is still used by the Armed forces of El Salvador and the Guatemalan Armed forces . Colt Model 653 M16A1 Carbine . 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 . Depending on whether it had a fixed or retractable buttstock and a forward assist , Colt labeled the M16A1 carbines the " Model 651 " , " 652 " , " 653 " , or " 654 " . All models used the M16A1 birdcage flash hider . 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 thousands of Model 653 M16A1 carbines , to the Israeli Defense Forces as part of Operation Nickel Grass . These Model 653s , which have also been called " CAR - 15s " by its users , continue to be in use with the IDF today . Some of the Model 653s in Israeli service have been heavily customized over the service years , such as having the barrel replaced or chopped down in length . They have been nicknamed Mekut ' zar or Mekut ' zrar . They are slowly being replaced with / or revamped to M4 carbine s . Colt also licensed Elisco Tools to produce the M16A1 carbine in the Philippines , who became a major user of the type , as the " Model 653P " . M4 Carbine . In the early 1980s , at the request of the United States Marine Corps , Colt upgraded the M16A1 rifle , resulting in the M16A2 rifle . Among the major changes were a reinforced lower receiver , a case deflector , a birdcage flash suppressor redesigned to be a muzzle brake , and a barrel with a faster 1 - in - 7 twist . The faster barrel was necessitated 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 M16A2 carbines . The " Model 723 " M16A2 carbine used the iron sights of the M16A1 , but had a case deflector . The barrel had a 1 - in - 7 twist , but the thinner profile of the older M16A1 carbine ' s barrel . 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 , the " C8 carbine " for use by the Canadian Forces . The original C8s were built by Colt as the " Model 725 " . In 1984 , the U . S . government asked Colt to develop a carbine with maximum commonality with the issue M16A2 . Colt named the carbine as the " XM4 " . The project would eventually culminate in the development and official adoption of the M4 carbine in 1994 . The United Arab Emirates ( UAE ) wished to purchase M16A2 carbines with the thicker M16A2 barrel , but still be able to mount the M203 grenade launcher . The M203 grenade launcher was designed for the thinner M16A1 barrel . A " step - cut " barrel was made , with a portion of the barrel thinned for the M203 mount . M16A2 carbines with A2 upper receivers and the step - cut barrel were designated " Model 727 " . These are often called " Abu Dhabi " carbines , in reference to the UAE ' s capital . The U . S . military also purchased several of these carbines prior to the official adoption of the M4 . GUU - 5 / P . The United States Air Force has made ad hoc upgrades to its GAU - 5 / As and GAU - 5A / As . The barrels and moderators were replaced with the longer 14 . 5 - inch barrel with a 1 - in - 12 twist , but the weapons retained their original designations . With the change to M855 cartridges , they either received 1 - in - 7 twist barrel or complete upper receiver assembly replacements . The GAU - 5 / A or GAU - 5A / A markings were removed and the weapons redesignated " GUU - 5 / P " . They also retain automatic fire instead of burst . The new designation more accurately reflected the weapon ' s place in the U . S . Air Force Aerospace Equipment Type Designation System ( AETDS ) . The weapons had initially been designated in the same format as aircraft guns , being placed in the GA category ( GA designating an aircraft gun , with U meaning unit , representing a complete system and not part of a kit ) , followed by the / A suffix meaning the system was for aircraft . GUU is the " guns , miscellaneous personal equipment " category , and the / P suffix indicating personal equipment . Colt Commando . Though Colt has focused its attention on carbines with 14 . 5 - inch barrels and rifles with 20 - inch barrels , Colt continues to make carbines with 11 . 5 - inch barrels , which it calls Commandos . Originally , Commandos were assembled from whatever spare parts are available , so " Model 733 " Commandos could have A1 - style upper receivers with case deflectors or A2 - style upper receivers , and M16A1 - profile 1 : 7 or M16A2 - profile 1 : 7 barrels . Depending on the specific models , Commandos may have had three - position fire control groups ( safe / semi - automatic / three - round burst ) , or four - position having both full - automatic and burst . The modern " Model 933 " has a " flattop " receiver , with a removable carrying handle and a MIL - STD - 1913 Picatinny rail , with semi - automatic and automatic fire . The " Model 935 " Commando has the features of the Model 933 , but has three - round burst fire instead of automatic . Though originally called the M16A2 Commando , Colt now markets them as the " M4 Commando " . The Colt Commando ' s 11 . 5 - inch barrel creates a substantially lower muzzle velocity and greater muzzle flash , in comparison to longer M16 carbines and rifles . The lower muzzle velocity may reduce wounding effects . In 2005 , Colt came out with a semi auto only version of the 733 . The designation of this rifle is the 6933 . Some American special operation forces , such as Army Special Operation Groups , used the M4 Commando in a limited capacity . Marine Force Recon personnel sometimes used M4 Commandos in place of their US M9 pistols . Currently , the Mk 18 Mod 0 with a 10 . 3 - inch barrel has taken the role of ultracompact carbine with the U . S . Navy SEALs . Police Use . Forms of the Colt commando are also used by police special forces groups around the world . Some of the users are BOPE . El Salvador National Civilian Police uses the M4 and its variants and Car - 15 and its variants in its regular police and special forces .