It is an externally powered, chain driven, single-barrel weapon which may be fired in semi-automatic, burst, 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 , depending on the type of ammunition used.
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 10,500 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.
Unlike most automatic firearm+s, the M242 does not depend on gas or recoil+ to actuate its firing system. Instead, it uses a 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 round+s.
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 two person team to install or remove the system (under ideal conditions) despite its considerable total weight.
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, limited only by the electrical drive speed (it cannot be fired faster than High rate); (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.
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 GAU-12 Equalizer+, the French+Giat M811+, or the Swiss+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.
#M791 Armour-piercing discarding sabot+ with Tracer
#*5.7 million rounds produced
#*The APDS-T penetrates lightly armored vehicles+, self-propelled artillery+, and aerial targets such as helicopter+s and various slow-moving, fixed-wing aircraft+.
#M792 High Explosive Incendiary with Tracer and Self Destruct
#*5.5 million rounds produced
#*The HEI-T can destroy unarmored vehicles and helicopters and suppress antitank missile positions and enemy squads out to a maximum effective range of 2,200 meters.
#M793 Target Practice with Tracer+
#*11.5 million rounds produced
#*The TP-T cartridge is a fixed-type, percussion-primed training round that matches the High Explosive Incendiary with Tracer (HEI-T MK210) round ballistically. The TP-T's tracer is visible out to 2,000 meters, however, the round has a maximum effective range (accuracy-limited) of 1,600 meters.
#M910 Target Practice Discarding Sabot with Tracer
#*The TPDS-T replicates the flight pattern of the M791 Armor Piercing Discarding Sabot+ with Tracer (APDS-T) round. The TPDS-T allows units to realistically practice sabot engagements.
#MK210 High Explosive Incendiary with Tracer
#*228,000 rounds produced
#*Used by the U. S. Navy in their Mk38 naval weapon system.
#M919 Armor-Piercing, Fin-Stabilized Discarding Sabot With Tracer.
#*The APFSDS-T round penetrates light armored vehicle+s, self-propelled artillery, and aerial targets, which includes helicopters and slow-moving fixed-wing aircraft. the dart is made of depleted uranium+.
Work on an upgraded weapon began in 1990. In doing so, all 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 Bradley Fighting Vehicle.
In 1977, the U. S. Navy+ realized that it needed a replacement for the Oerlikon+ 20mm Mk 16 series of guns. In 1986, this requirement 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.
M242 Bushmaster+ The M242 Bushmaster is a 25 mm (25×137mm) 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 combat vehicles and watercraft.