M242 25mm Automatic Gun

Gary's Combat Vehicle Reference Guide

The M242 is an electrically powered, chain driven, automatic weapon. It can destroy lightly armored vehicles and aerial targets such as helicopters and slow-flying aircraft. It can also suppress enemy positions such as troops in the open, dug-in positions, and built-up areas.

The M242 is fed by a metallic link belt and has dual-feed capability which allows the crew to select and load two types of available service ammunition. The M242 fires both European and U.S. 25mm ammunition. The five basic U.S. rounds used with the M242 include the M791, M792, M793, M910, and M919.

The gun can be installed or removed in three parts:

• Receiver assembly. 94.8 lb (43 kg).
• Barrel assembly. 89.9 lb (40.8 kg).
• Feeder assembly. 57.8 lb (26.2 kg).

The M242 is the primary armament on the U.S. Army M2/M3 series Bradley Fighting Vehicle and the U.S. Marine Corp LAV-25.

Enhanced 25mm Gun

The enhanced 25mm gun has three major components: a chrome-lined barrel, an enhanced feeder, and an enhanced receiver. The gun also has quick-detachable link covers, a larger breach assembly, longer recoil, and a triple-spring drive clutch. It also has a built-in test (BIT) for the feed-select solenoid and 1.0-horsepower gun-drive motor.

The dual-feed system uses sprockets and extractor grooves to control rounds. A system of clutches allows either ammunition belt sprocket to engage and feed a round. A single 1.5-horsepower DC motor externally powers the gun. The enhanced gun uses a 1.0-horsepower DC motor. The gunner can choose from three rates of fire:

1. Single Shot. The commander or gunner can shoot about as fast as he can squeeze the trigger.
2. Low Rate. The commander or gunner can shoot 100 rounds a minute, plus or minus 25 rounds.
3. High Rate. The commander or gunner can shoot 200 rounds a minute, plus or minus 25 rounds.

The M242 gun has eight cycles of function:

1. Sear or Charge Cycle. The 25mm bolt is forward of its rearmost position. The sear engages the master link. As a safety measure, the firing pin remains uncocked.
   
   
2. Feed Cycle. Linked ammunition enters the 25mm gun feeder. The feed sprockets strip the rounds from the links and move the round into the round positioner one at a time. The round positioner pushes the round into the ready position. During the feed cycle, the bolt moves about 25mm to the rear of the sear position. The feeder rotor rotates one-third of a turn, allowing the round positioner to place a round into the rotor. Absolute hang-fire protection activates in this position.
   
   
3. Chamber or Ram Cycle. The rotor stops moving counterclockwise once the round is positioned on the bolt face. The bolt, bolt carrier, and round move forward until the round seats fully in the chamber.
   
   
4. Lock Cycle. The bolt is in the full forward position and the bolt carrier is still moving forward. The cam pin moving in its channel causes the bolt to rotate counterclockwise. This allows the lugs on the bolt to engage in the recesses of the breech, making a solid lock.
   
   
5. Fire Cycle. The final rotation of the bolt pushes the firing pin tang off the firing pin pawl in the track assembly. This causes the firing pin spring to push the firing pin forward. In its full forward position, the firing pin's tip protrudes 2 millimeters through the bolt face. The indicator arrow points to FIRE. Although the gun requires no gas to operate, it does use 12 mm of recoil to deactivate mechanical interlock. If the breech fails to recoil, the gun stops cycling with the bolt still locked in the breech.
   
   
6. Unlock Cycle. Once past the MISFIRE position, the master link and slider start to the rear. The slider pulls the bolt carrier with it. The cam pin rotates the bolt clockwise, causing it to unlock from the recesses in the breech.
   
   
7. Extract Cycle. As the bolt moves to the rear, the fixed T-slot extractors remove the cartridge case from the chamber. The case remains positioned on the face of the bolt. The bolt continues to the rear until it locks in the sear position.
   
   
8. Eject Cycle. The expended case remains in the bolt face until the gunner pulls the trigger to fire another round. When that happens, the bolt moves to the FEED position. The rotor rotates one-third of a turn, feeding a round onto the bolt face and sweeping the expended case into the feeder ejection chute. As the bolt moves forward to chamber the round, the eject arm on the bolt carrier pushes the expended case from the receiver cartridge eject port.

The U.S. adopted the 25 mm Oerlikon Type KBA ammunition for use in the M242 gun. Developed by Oerlikon in the 1960's, this high-performance cartridge can be recognized by the annular link-positioning groove located 98.5 mm from the base of the steel cartridge case. This groove disappears when the cartridge is fired but leaves an impression on the case. HEI-T, APDS-T, and multipurpose projectiles are available.

Cartridge data for 25mm ammunition.

Designations	25x137, 25 mm Oerlikon Type KBA
Country of Origin	Switzerland
Case Type	Rimless
Case Length	136.5 mm
Rim Diameter	37.8 mm
Head Diameter	38.0 mm
Shoulder Diameter	35.5 mm
Mouth Diameter	26.1 mm
Projectile Bourrelet Diameter	24.8 mm
Cartridge Length	223 mm
Primer Type	Percussion
The cartridge case has an annular link-positioning groove 98.5 mm from the base of the case.

Ballistic data for 25mm ammunition.

	M791 APDS-T	M792 HEI-T	M793 TP-T	M910 TPDS-T	M919 APFSDS-T
Muzzle Velocity	4,413 fps (1,345 mps)	3,609 fps (1,100 mps)	3,609 fps (1,100 mps)	5,003 fps (1,525 mps)	4,544 fps (1,385 mps)
Time of Flight (seconds) 1,000 meters 1,500 meters 2,000 meters 2,500 meters	0.8 1.2 1.7 2.2	1.2 2.2 3.6 5.3	1.2 2.2 3.5 5.2	0.7 1.2 1.8 2.5	0.8 1.2 1.6 2.1
Cartridge Weight	16.15 oz (458 g)	17.67 oz (501 g)	17.67 oz (501 g)	14.81 oz (420 g)	16.01 oz (454 g)
Projectile Weight	4.73 oz (134 g)	6.53 oz (185 g)	6.42 oz (182 g)	3.35 oz (95 g)	3.39 oz (96 g)
Propellant	Radford AP225	WC 890	WC 890	Expro XPR51C4	Hercules HES9053
Primer	M115 percussion				M115 Mod A percussion
Tracer Burn Time (seconds)	>1.7	>3.5	>3.5	>1.8	>1.8
Bursting Radius Arming Distance	N/A	16 ft (5 m) 33 to 656 ft (10 to 200 m)	N/A	N/A	N/A
Max Effective Range	6,562 ft (2,000 m)	9,842 ft (3,000 m)	5,249 ft (1,600 m)	6,562 ft (2,000 m)	8,202 ft (2,500 m)
Tracer Burn Range	>6,562 ft (>2,000 m)	>6,562 ft (>2,000 m)	>6,562 ft (>2,000 m)	>6,562 ft (>2,000 m)	>8,202 ft (>2,500 m)
	M791 APDS-T	M792 HEI-T	M793 TP-T	M910 TPDS-T	M919 APFSDS-T

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M791 Armor-Piercing Discarding Sabot with Tracer (APDS-T)

The M791 APDS-T penetrates lightly armored vehicles, self-propelled artillery, and aerial targets such as helicopters and slow-moving, fixed-wing aircraft.

The APDS-T is a fixed-type, percussion, primed round. It consists of a sabot-encapsulated projectile body crimped to a steel cartridge case. The projectile body consists of a solid tungsten alloy penetrator, pressed-on aluminum windscreen, pressed-in tracer pellets, molded discarding-type nylon sabot, staked aluminum base, and welded or pressed-on nylon nose-cap. The projectile sabot and nose-cap are black with white markings.

Gasses produced by the burning propellant send the projectile from the gun at 1,345 meters per second (plus or minus 20 meters per second) and ignite the tracer. Setback, centrifugal, and aerodynamic forces cause both the sabot and nose-cap to discard as soon as the round leaves the barrel. The projectile is spin-stabilized and penetrates the target solely by kinetic energy.

The discarding sabot leaves the barrel at about a 34° angle along the gun-target line (17° off each side) for 100 meters.

The maximum effective range is 2,000 meters due to tracer burnout. Although its tracer burns out at 2,000 meters, an APDS-T round is accurate out to 2,200 meters. As the range increases, the APDS-T penetration decreases, especially when target vehicles have applique armor (an added layer of armor).

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M792 High-Explosive Incendiary with Tracer (HEI-T)

The M792 HEI-T can destroy unarmored vehicles and helicopters and suppress anti-tank guided missile (ATGM) positions and enemy squads beyond coax range (900 meters) and out to a maximum effective range of 3,000 meters.

The HEI-T cartridge is a fixed-type, percussion-primed round. The one-piece projectile body contains HEI and is crimped onto a steel cartridge case. The hollowed steel projectile houses an M758 mechanical fuze, 32 grams of an HEI mix, and a pressed-in tracer. The projectile is yellow with a red band, black markings, and a gold tip. On some rounds, the projectile's yellow color is slightly orange near the red band.

Gasses produced by the burning propellant send the projectile out of the gun at 1,100 meters per second (plus or minus 20 meters per second). On impact, the M758 mechanical fuze ignites and the HEI filler detonates. This projects steel fragments from the body, rotating band assembly, and incendiary filler over a 5-meter radius.

The maximum effective range for HEI-T rounds is 3,000 meters, at which range, a mechanical fuze (the M758) detonates the round. Accuracy decreases beyond 1,600 meters, and the tracer burns out at 2,000 meters. However, the round's 5-meter bursting radius and rate of fire let the firer engage either point or area targets out to the maximum effective range.

The M792 HEI-T projectile can detonate in any of three ways:

1. Direct Impact. Striking the target crushes the projectile's probe cap. This pushes the probe rearward, which thrusts the firing pin into the detonator, which detonates the HEI mixture.
2. Grazing Impact. Due to spin decay (loss of forward velocity), the projectile strikes the target with insufficient force. Spin decay triggers the setback spring to overcome centrifugal force, pushes the body assembly forward, and thrusts the detonator into the firing pin.
3. Self-Destruct. If it does not hit a target, the projectile self-destructs at 3,000 meters. However, head and tail winds, depending on their severity, can reduce the distance at which the round self-destructs.

Type Classification Date: 1980. Unit cost: $49 (Fiscal Year 2007).

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M793 Target Practice with Tracer (TP-T)

The M793 TP-T cartridge is a fixed-type, percussion-primed training round with M28 link that matches the M792 HEI-T round ballistically.

The projectile consists of a hollow steel body with blue with white markings. The TP-T's maximum effective range is 1,600 meters, and the tracer is visible out to 2,000 meters. However, accuracy is greatly reduced beyond 1,600 meters.

This is a training item and is not used in combat.

Type Classification Date: 1979. Unit cost: $17 (Fiscal Year 2004/2005).

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M794 Dummy

The M794 dummy cartridge is used for non-firing system checkout for the M242 25mm automatic cannon and training of the crew.

The cartridge is a modified M793 target practice with tracer (TP-T) projectile silver brazed to a modified standard cartridge case and is completely inert. The cartridge case cavity is filled through an enlarged primer hole with an epoxy resin filler to approximate the weight of the M792 high explosive incendiary-tracer and M793 TP-T service cartridges. The threaded nose of the TP-T projectile is silver brazed to the projectile body to improve physical integrity. The external configuration of the M794 metal dummy cartridge (by use of standard components) is the same as that of the M792 HEI-T and M793 TP-T service cartridges. These cartridges are linked together by the M28 link.

This is a training item and is not used in combat.

Type Classification Date: December 1981. Unit cost: $36 (Fiscal Year 2007).

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M910 Target Practice Discarding Sabot with Tracer (TPDS-T)

The target-practice, discarding sabot with tracer (TPDS-T) replicates the flight pattern of the M791 APDS-T round. The TPDS-T allows units to practice sabot engagements on limited-distance ranges. The maximum range of the TPDS-T is 6,404 meters.

The TPDS-T cartridge is a fixed type, percussion-primed round. It consists of a sabot-projectile assembly crimped to a steel cartridge case. The projectile assembly includes a disposable aluminum pusher base. It also includes a subprojectile encapsulated with a discarding nylon sabot and polyethylene protective cap. The subprojectile has a steel core with either an aluminum or a steel windscreen and with pressed-in tracer pellets. The projectile is blue with white markings.

Gases produced by the burning propellant discharge the projectile from the gun at 1,540 meters per second (plus or minus 20 meters per second) and ignite the tracer. Setback, centrifugal force, and air pressure cause the sabot to discard on leaving the gun barrel. The projectile is spin-stabilized and penetrates the target solely by kinetic energy.

The discarding sabot may cause death or injury along a 34° angle along the gun-target line for 100 meters.

The TPDS-T cartridge trajectory ballistically matches the APDS-T plus or minus 1 mil to a range of 2,000 meters. The tracer burns out at 2,000 meters.

Type Classification Date: 1988. Unit cost: $16 (Fiscal Year 2004/2005).

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M910E1 Target Practice Discarding Sabot with Tracer (TPDS-T)

The M910E1 will provide an improved target practice cartridge for the M919 APFSDS-T cartridge. The trajectory will be ballistically similar to the M919 and possess a similar tracer signature to the M919 cartridge when viewed through the Bradley Fighting Vehicle's Improved Bradley Acquisition System. The M910E1 will replace the current M910 TPDS-T cartridge (designed to be ballistically similar to the M791) as the training round for both the M919 and the M791.

The M919 service cartridge contains a DU penetrator and is not used for training. The M919 and M791 service cartridges exceed the maximum range requirement for most training ranges.

This is a training item and is not used in combat.

Type Classification Date: Limited Production, November 2004. Standard, May 2005. Unit cost: $20 (Fiscal Year 2004/2005).

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M919 Armor-Piercing, Fin-Stabilized Discarding Sabot With Tracer (APFSDS-T)

The armor-piercing, fin-stabilized discarding sabot with tracer (APFSDS-T) round penetrates lightly armored vehicles, self-propelled artillery, and aerial targets, which includes helicopters and slow-moving fixed-wing aircraft.

The APFSDS-T is a fixed-type, percussion primed round that consists of a sabot-encapsulated projectile crimped into a steel cartridge case. The projectile is made of slate gray, corrosion-protected, depleted uranium. It has a screw-on steel fin with pressed-in tracer pellets; a three-piece, segmented aluminum sabot and a snap-on plastic protective cap. The projectile sabot and protective nose-cap are black, and the slip-band nylon obturator is white. The round has a green rubber sealant between the sabot segments, the sabot and penetrator, and the sabot and the plastic cap.

Gases produced by the burning propellant discharge the projectile from the gun at 1,385 meters per second (plus or minus 20 meters per second) and ignite the tracer. Setback, centrifugal force, and air pressure cause the sabot to discard on leaving the gun barrel. The projectile is fin-stabilized and penetrates the target solely by kinetic energy.

The discarding sabot leaves the barrel at a 17° angle on both sides of the gun-target line for 100 meters (total of 34°).

The M919 APFSDS-T round has greater effective range, penetration capabilities, and tracer burn time than the APDS-T (M791).

The M919 replaces the M791 as the primary armor-piercing cartridge for use in the 25mm M242 Bushmaster. The M919 cartridge significantly increases the lethality of the M242 against all threat infantry fighting vehicles. The M791 does not defeat the existing threat. The M919 state-of-the-art armor defeat mechanism, combined with a high muzzle velocity, yields a very high kill probability for firing at stationary and moving threat targets. The M919 is the only 25mm "long-rod" penetrator produced for the M242 cannon. The M919 provides the soldier greater standoff, thus increasing battlefield survivability for the vehicle and accompanying infantry. The M919 provides the soldier with the lethality needed to defeat the enemy, accomplish the mission, and to survive on today's modern battlefield.

Exposure to M919 ammunition results in exposure to low level radiation. The amount of radiation the soldier receives is proportional to the amount of time spent in the vicinity of M919 ammunition. Although the radiation exposure received is low and considered safe, avoid unnecessary contact with packaged APFSDS-T M919 ammunition, within mission constraints.

Type Classification Date: Limited Production Urgent, September 1989. Standard, September 1993. Unit cost: $98 (Fiscal Year 2004/2005).

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XM1021 Break-Up Cartridge

The XM1021 utilizes a projectile with a plastic jacket loaded with pressed iron powder tablets in the main body and polystyrene foam in the nose. Upon firing of the Break-up cartridge, the projectile jackets ruptures and the iron powder and the projectile jacket fall to the ground within 75-100 meters from the weapon. Neither a test facility with bullet trap nor a full scale range is necessary to perform the verification functional check prior to deployment.

M242 Gun Prime Item Specification approved: January 1997.

The M28 25mm cartridge link is a two-piece hardened steel assembly (main and pivot links) intended to hold and link the ammunition for guiding through the weapon system. The Swiss Gerlikon link and the M28 are dimensionally identical.

The 25mm gun's impact on typical urban targets seems magnified if the firing is in short bursts. At close ranges, the gunner might need to shift his point of aim in a spiral pattern to ensure that the second and third bursts enlarge the hole. Even without burst fire, sustained 25mm gunfire can defeat almost all urban targets:

• Reinforced Concrete. Reinforced concrete walls, which are 12 to 20 inches thick, present problems for the 25mm gun when trying to create breach holes. It is relatively easy to penetrate, fracture, and clear away the concrete, but the reinforcing rods remain in place. These create a "jail window" effect by preventing entry but allowing grenades or rifle fire to be placed behind the wall. Steel reinforcing rods are normally 3/4 inch thick and 6 to 8 inches apart - there is no quick way of cutting these rods. They can be cut with demolition charges, cutting torches, or special power saws. Firing with either APDS-T or HEI-T rounds from the 25mm gun will not always cut these rods.
  
  
• Brick Walls. The 25mm gun more easily defeats brick walls, regardless of their thickness, and the rounds produce the most spall.
  
  
• Bunker Walls.The 25mm gun is devastating when fired against sandbag bunker walls. Obliquity has the least affect on the penetration of bunker walls. Bunkers with earth walls up to 36 inches thick are easily penetrated. At short ranges typical of combat in urban areas, defeating a bunker should be easy, especially if the 25mm gun can fire at an aperture.

Although the penetration achieved by the two combat rounds - armor-piercing, discarding sabot with tracer (APDS-T) and high explosive, incendiary with tracer (HEI-T) - differ slightly, both are eventually effective. However, the best target results are not achieved with either of the combat rounds. At close range against structural targets, the training round (TP-T) is significantly more effective. The TP-T round, however, has little utility when used against enemy armored vehicles.

• APDS-T. The APDS-T round penetrates urban targets by retaining its kinetic energy and blasting a small hole deep into the target. The APDS-T round gives the best effects behind the wall, and the armor-piercing core often breaks into two or three fragments, which can create multiple enemy casualties. The APDS-T needs as few as four rounds to achieve lethal results behind walls.
  
  The APDS-T round can penetrate over 16 inches of reinforced concrete with enough energy left to cause enemy casualties. It penetrates through both sides of a wood frame or brick veneer building. Field fortifications are easily penetrated by APDS-T rounds.
  
  
• HEI-T. The HEI-T round penetrates urban targets by blasting away chunks of material. The HEI-T round does not penetrate an urban target as well as the APDS-T, but it creates the effect of stripping away a greater amount of material for each round. The HEI-T does more damage to an urban target when fired in multiple short bursts because the accumulative impact of multiple rounds is greater than the sum of individual rounds.
  
  The HEI-T round does not provide single-round perforation or incapacitating fragments on any external masonry structural wall. It can create first-round fragments behind wood frame and brick veneer walls. HEI-T rounds cannot penetrate a bunker as quickly as APDS-T, but they can create more damage inside the bunker once the external earth has been stripped away. Against a heavy bunker, about 40 rounds of HEI-T are needed to strip away the external earth shielding and breach the inner lining of concrete or timber. The HEI-T round is also used for suppression against known or suspected firing ports such as doors, windows, and loopholes.