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M2
An M2 machine gun surrounded by spent round casings
Type	Heavy machine gun
Place of origin	United States of America
Service history
In service	1932–present
Used by	See text
Wars	World War II, Cold War, modern, Desert Storm, Iraqi Freedom
Production history
Designed	1921
Produced	1932—
Specifications
Weight	38 kg (58 kg w/ tripod)
Length	1,650 mm (65 in)
Barrel length	1,140 mm (44⅞ in)
Cartridge	.50 BMG
Caliber	.50 in (12.7 mm)
Action	Recoil-operated; short recoil
Rate of fire	500 round/min
Muzzle velocity	3,050 ft/s (930 m/s)
Effective range	1,800 m (2,200 yd)
Feed system	Belt-fed

This article is about the .50 caliber M2 machine gun. For the .30-06 M2 machine gun, see M1919 Browning machine gun.

The M2 Machine Gun, or Browning .50 Caliber Machine Gun is a heavy machine gun designed towards the end of World War I by John Browning. It was nicknamed Ma Deuce by US troops or simply called "fifty-cal" in reference to its caliber. The design has had many specific designations; the official designation for the current infantry type is Browning Machine Gun, Cal. .50, M2, HB, Flexible.

The Browning .50 machine gun has been used extensively as a vehicle weapon and for aircraft armament by the United States from the 1920s to the present day. It was heavily used during World War II, the Korean War, the Vietnam War, as well as during operations in Iraq in the 1990s and 2000s. It is the primary heavy machine gun of NATO countries, and has been used by many other countries. It is still in use today. It was very similar in design to the smaller Browning Model 1919 machine gun .30-06 Springfield.

[edit] History

Using a round originally designed by Winchester, the .50 BMG round was designed as a response to the German 13mm anti-tank rifle of World War I and employed in a redesigned and scaled-up M1917 Browning .30 cal. machine gun. It was quickly adapted to the anti-aircraft role. It was also selected for the ground role and adopted by the U.S. as the Model 1921. The latter served during the 1920s as an anti-aircraft and anti-armor gun. In 1932, the design was updated and adopted as the M2, though fulfilling the same role. As with the M1921, the original infantry variant of the M2 was equipped with a water jacket for cooling [1]. A variant without a water jacket, but with a thicker-walled, air-cooled barrel superseded it (air-cooled barrels had already been used on variants for use on aircraft, but these quickly overheated in ground use). The added mass and surface area of the new barrel compensated, somewhat, for the loss of water-cooling, while reducing bulk and weight (the M2 weighed 121 lbs, with water, whereas the M2 HB weighs 84 lbs). This new variant was the designated the M2 HB (HB for Heavy Barrel). Due to the long procedure for changing the barrel, an improved system was developed called QCB (quick change barrel). A lightweight version, weighing 24 lb (11 kg) less—a mere 60 lb (27 kg)—was also developed.

[edit] Design

The M2 is a scaled-up version of John Browning's M1917 .30 caliber machine gun (even using the same timing gauges), and fires the .50 BMG cartridge, which today is also used in high-powered sniper rifles and long range target rifles due to its excellent long range accuracy, external ballistics performance, incredible stopping power, and lethality. The M2 is an air-cooled, belt-fed, machine gun that fires from a closed bolt, operated on the short recoil principle. In this action, the bolt and barrel are initially locked together, and recoil upon firing. After a short distance, the bolt and barrel unlock, and the bolt continues to move rearwards relative to the barrel. This action opens the bolt, and pulls the belt of ammunition through the weapon, readying it to fire again, all at a cyclic rate of 450–550 rounds per minute (600–1,200 M2/M3 in WW2 aircraft, 300 synchronized M2). This is a rate of fire not generally achieved in use, as sustained fire at that rate will "shoot out" the barrel within a few thousand rounds, necessitating replacement. The M2 machine gun's sustained rate of fire is considered to be anything less than 40 rounds per minute.

The M2 has a maximum range of 7.4 kilometers (4.2 miles) when using the M2 ball ammunition, with a maximum effective range of 1.8 kilometers (1.2 miles) when fired from the M3 tripod. In its ground-portable, crew-served role, the gun itself weighs in at a hefty 84 pounds (38 kg), and the assembled M3 tripod another 44 pounds (20 kg). In this configuration, the V-shaped "butterfly" trigger is located at the very rear of the weapon, with a "spade handle" hand-grip on either side of it and the bolt release the center. The "spade handles" are gripped and the butterfly trigger is depressed with one or both thumbs. When the bolt release is locked down by the bolt latch release lock on the buffer tube sleeve, the gun functions as a fully automatic weapon. in the down position, the weapon is in full automatic fire mode. The bolt release can be locked into the up position resulting in semi-automatic firing. In either mode the gun is fired by pressing the butterfly triggers. Recently new rear buffer assemblies have used squeeze triggers mounted to the hand grips doing away with the butterfly triggers.

Because the M2 was intentionally designed to be fit into many configurations, it can be adapted to feed in rounds from the left or right side of the weapon by exchanging the belt-holding pawls, the belt feed pawl, the front and rear cartridge stops, and reversing the bolt switch. The conversion can be completed in under a minute with no tools.

When firing blanks, a large blank-firing adapter (BFA) must be used to keep the gas pressure high enough to allow the action to cycle. The adapter is very distinctive, attaching to the muzzle with three rods extending back to the base. The BFA can often be seen on M2s during peacetime operations.

[edit] Combat usage

The M2 .50 Browning machine gun is used for various roles:

• A medium infantry support weapon
• When doubled it is used as an anti-aircraft gun in some ships, or on the ground. In these cases, one M2 with a left-handed feed and one with right-handed feed are paired. Four and six guns are also sometimes mounted on the same turret.
• Primary or secondary weapon on an armored fighting vehicle.
• Primary or secondary weapon on a naval patrol boat.
• Secondary weapon for anti-boat defense on naval destroyers, frigates and aircraft carriers.
• Coaxial gun or independent mounting in some tanks.
• Fixed-mounted primary armament in WWII-era U.S. aircraft such as the P-47 Thunderbolt, P-51 Mustang, and the Korean-era U.S. F-86 Sabre.
• Fixed or flexible-mounted defensive armament in WWII-era bombers such as the B-17 Flying Fortress, and B-24 Liberator.
• A long-range sniper rifle, when equipped with a telescopic sight. This use was discovered by US Marine sniper Carlos Hathcock during the Vietnam War. The M2 had two traits that made this possible

1. The M2HB has a full automatic mode activated by locking down the bolt release lever between the butterfly triggers. Full automatic fire mode is achieved is rotating a snap spring on the exterior of the buffer housing to hold the bolt release down. The M2HB can be fired dependably in semiautomatic mode with the bolt release up and pressing it to load each round. A skilled gunner can can fire single rounds by quickly releasing the butterfies on full automatic mode. In either mode the gun is fired by pressing the butterfly trigger.
2. Its traversing-and-elevating (T & E) tripod made accurate aiming possible, by turning two knobs until the target was in the sights.

Using the Unertl scope supplied on his Winchester Model 70 30.06 sniper rifle and a mounting bracket of his own design, Hathcock could quickly convert the M2 into a rifle that, in single-fire mode, could accurately hit targets at up to 2500 yards--twice the range of the Winchester sniper rifle. The success of the M2 in this role led to the development of purpose-built sniper rifles, generally bolt-action, designed to fire the same .50-caliber round.

A water-cooled version of the larger M2 was used as an emplaced or vehicle-mounted anti-aircraft weapon on a sturdy pedestal mount.

Commonwealth use of the .50 was limited in the Second World War, despite it being standard armament on US-built/designed AFVs such as the M4 Sherman or M10 Wolverine that began to see use in British, Canadian, Australian and New Zealand units from 1942 on. Commonwealth tank crew commanders more often than not deleted the .50 altogether as being of limited use, given several factors. Primarily, the weapon was an anti-aircraft weapon, and Allied aerial superiority precluded its necessity. As well, in order to employ the weapon against ground targets, the commander had to exit the turret and expose himself to enemy fire. Commanders—especially in Italy—also found that the gun caught on low-hanging trees and vines and posed a danger to the crew commander's head and face.

[edit] Variants and derivatives

Naval twin-mounting