M242 Bushmaster The M242 Bushmaster is a 25 mm ( 25x137mm ) chain - fed autocannon . It is used extensively by the US armed forces , as well as by NATO ' s and some other nations ' forces in ground vehicles and watercraft . It is an externally powered , chain driven , single - barrel weapon which may be fired in semi - automatic or automatic modes . It is fed by a metallic link belt and has dual - feed capability . The term " chain gun " derives from the use of a roller chain that drives the bolt back and forth . The gun can destroy lightly armored vehicles and aerial targets ( such as helicopters and slow - flying aircraft ) . It can also suppress enemy positions such as exposed troops , dug - in positions , and occupied built - up areas . The standard rate of fire is 200 rounds per minute . The weapon has an effective range of 3 , 000 meters , depending on the type of ammunition used . The weapon was designed and originally manufactured by McDonnell Douglas ( later acquired by the Boeing Corporation ) ; however it is now produced by Alliant Techsystems ( ATK ) of Mesa , Arizona . History . The Bushmaster project started as an offshoot of the US Army ' s MICV - 65 program that was attempting to introduce a new infantry fighting vehicle to replace their existing M113 s . Part of this program called for a new scout vehicle to replace the M114 , a parallel development taking place under the XM800 Armored Reconnaissance Scout Vehicle . Both the XM800 and the cavalry version of the XM701 MICV vehicles were armed with the M139 , a US - built version of the Hispano - Suiza HS . 820 20 mm autocannon . During the testing phase the Army eventually rejected the XM701 and started work on a newer design known as the XM723 . Soon after the XM800 was also rejected . This led to the combination of the two programs , moving the scout role to the cavalry version of the XM723 . At the same time , the M139 proved to be disappointing and a contract for a new weapon to replace it started in 1972 at Hughes Aircraft as the Vehicle Rapid - Fire Weapons System - Successor , or VRFWS - S . This was essentially a power - driven gun firing similar ammunition as the HS . 820 , the power driven mechanism would ensure operation even in the case of a misfire . Progress on the VRFWS - S was slow , and eventually resulted in a switch to a much more powerful 25 mm round . Similar delays in the MICV program meant the ultimate vehicles descending from their efforts , the M2 / M3 Bradley Fighting Vehicle , did not enter production until 1981 , by which point the Bushmaster had matured . Since 1990 , there have been several enhancements made upon the weapon , resulting in the Enhanced 25 mm gun . To date , more than 10 , 000 weapons are in service . One of the major reasons for this popularity is the extremely reliable nature of the weapon . It has a rating of 22 , 000 mean rounds between failure ( MRBF ) , much higher than many comparable devices . Description . Unlike most automatic firearm s , the M242 does not depend on gas or recoil to actuate its firing system . Instead , it uses a 1 . 0 hp ( 750 W ) DC motor , positioned in the receiver to drive the chain and dual - feed system . This system uses sprockets and extractor grooves to feed , load , fire , extract , and eject rounds . A system of clutches provides for an alternate sprocket to engage and thus allows the gunner to switch between armor piercing and high explosive rounds . The weapon assembly consists of three parts : the barrel assembly , the feeder assembly , and the receiver assembly . The three - part structure makes it possible for a single person to install or remove the system despite its considerable total weight . Ammunition . A wide range of ammunition has been developed for this weapon , providing it with the capability to defeat the majority of armored vehicles it is likely to encounter , up to and including some tank s . The ammunition used in the M242 may also be used in a variety of weapons such as the French Giat M811 , the GAU - 12 , or the Oerlikon KBA weapon system . It has the capability to fire U . S . manufactured ammunition as well as the NATO equivalents thereof . Primarily though , it fires six types of rounds : the M791 , M792 , M793 , M910 , MK210 , and M919 . Variations . The M242 is currently in use by the United States Army , Navy , Marine Corps , and Coast Guard , the New Zealand Army , Royal New Zealand Navy , the Norwegian Army , the Spanish Army , the Swiss Army , the Canadian Army , the Australian Army and Navy , the Irish Navy , the Israeli Navy , the Singapore Army and Republic of Singapore Navy as well as several others . The wide usage results in several variations and modifications on the standard M242 weapon system . Ground Vehicles . The M242 is standard equipment on the U . S . Army M2 and M3 Bradley fighting vehicles . It is also in use on the LAV - 25 . Currently , the Bushmaster II 30 mm chain gun ( a successor to the M242 ) is also in use on the Marine Corps ' Expeditionary Fighting Vehicle ( EFV ) . The M242 is also a popular choice of primary armament for armoured fighting vehicle s manufactured around the world , such as the Bionix AFV and Singapore ' s upgraded M113 " ULTRA " OWS . Enhanced 25 mm gun . Work on an upgraded weapon began in 1990 . In doing so , three major systems and seven minor systems were improved . The modifications began with introducing a chrome - lined barrel , an enhanced feeder , and an enhanced receiver . The weapon systems also received minor upgrades such as quick - detachable link covers , a larger breech assembly , a high efficiency muzzle brake , longer recoil , an integral round counter , an extended life firing pin and spring , and a triple - spring drive clutch . It was first put to use on the M2A3 Bradley , the third version of the M2 Infantry Fighting Vehicle . Aircraft . The M242 is not used on aircraft . The AC - 130U and the AV - 8 Harrier II use a different 25 mm weapon , the 5 - barrel GAU - 12 / U . The sister weapon of the M242 , the M230 30 mm chain gun , is standard equipment on the AH - 64 Apache attack helicopter . Naval . In 1977 the U . S . Navy realized that it needed a replacement for the Oerlikon / Hispano - Suiza 20mm Mk 16 series of guns . In 1986 this need was satisfied with the introduction of the Mk 38 Mod 0 weapons system . A derivative of the M242 system , the Mk 38 consists of the M242 chain gun and the Mk 88 Mod 0 machine gun mount . It provides ships with defensive and offensive gunfire capability for the engagement of a variety of surface targets . Designed primarily as a close - range defensive measure , it provides protection against patrol boat s , floating mines , and various shore - based targets . The US Navy also developed a high ROF variant under the designation Mk 46 Mod 0 . Recently , several US Navy platforms have been outfitted with a newer version , Mk 38 Mod 2 which is remotley operated and includes an Electronic Optical Sight , Laser Range - Finder , FLIR , and a more reliable feeding system , enhancing the weapon systems capabilities and accuracy . In 2006 the Sri Lanka Navy added M242 to its fleet of Fast Attack Craft In the Republic of Singapore Navy , stabilised M242 guns are also adapted using Israeli ' s Typhoon system , on remote - controlled rigid - hull vessel . These were deployed as part of coalition forces ' port security efforts in Iraq as well as anti - piracy roles in the Gulf of Aden . Operation . The M242 weapon system has both electrical and manual fire control and can be operated electrically or manually . In doing so , the gunner can choose from three rates of fire : ( 1 ) Single Shot Semi - Automatic , in which the gunner can shoot as fast as the trigger can be operated ; ( 2 ) Low Rate Fully Automatic , in which the weapon fires 100 rounds a minute , plus or minus 25 rounds ; and ( 3 ) High Rate Fully Automatic , in which the weapon fires 200 rounds a minute , plus or minus 25 rounds .