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Ordnance Notes -- by Bob Stoner GMCM(SW) Ret.
AN/M-2 HB .50 Browning Machineguns
The venerable .50 Browning machinegun has been
standard issue with the American armed forces since 1921. It has appeared
in water-cooled anti-aircraft, air-cooled aircraft (flexible and fixed), and
air-cooled
ground (heavy barrel) configurations.
The AN/M2 gun is the direct descendent of the M1921. The receiver of the
gun is the starting point for the above versions. In addition, the gun
can be setup to feed from either the left or right sides and can be fired manually
or electrically. The AN/M3 is a modification of the AN/M2 which will be
described later. The gun can be setup to fire full automatic or both semi
auto and full auto by the addition of some parts.
AN/M2 .50 BMG Water-cooled
The .50 BMG water-cooled resembles a scaled-up
.30 BMG M1917A1. It uses a light weight barrel surrounded by a barrel
jacket filled with a 60/40 mix of water and ethylene glycol. A packing
on the rear of the barrel seals in the water/antifreeze mix at the rear
and a packing at the muzzle end of the barrel (muzzle gland) seals in the water/antifreeze
mix at the front. The barrel support in the trunnion block is brass, as
is the front of the water jacket, to minimize corrosion . The water jacket
itself is Parkerized (manganese phosphated). The water jacket is provided
with two ports for connection of hoses and a condenser. As the gun fires
continuously, the water reaches a point where it would boil away. However,
the steam is routed through a condenser to cool it down until it becomes water
again. The water is recirculated to the water jacket by convection. Weight
of the gun with a full water jacket is 121 pounds. Because the .50 BMG is water-cooled,
it can theoretically never overheat (as long as there is water in the jacket).
Water-cooling prolongs the life of the barrel, especially when long, withering
bursts of fire are the norm. As a result, the .50 BMG water-cooled was
the primary light anti-aircraft gun until it was replaced by the 20mm Oerlikon
in U.S. Naval service (1942). It was replaced in U.S. Army service by
the AN/M2HB for anti-aircraft and ground tasks (mid-1942, early 1943).
Most AN/M2 .50 BMG water-cooled guns were converted to either aircraft or ground
guns as World War 2 progressed. The water-cooled type is obsolete and is likely
to be encountered only in museums.
AN/M2 .50 BMG Air-cooled (aircraft)
The .50 BMG air-cooled aircraft gun was THE
major machinegun used by all services' fighters and bombers (and motor torpedo
boats) during WW2. Early attempts to replace it with 20mm designs, most
notably the Hispano-Suiza HS404, did not work out until after the war ended.
Early HS404 designs became the AN/M1 and AN/M2 20mm aircraft machineguns which
were deemed unsuccessful by the users. After WW2 ended, the product-improved
20mm AN/M3, M24, and Mk12 guns became standard. As these guns gained ascendancy,
the .50 BMG aircraft gun diminished in importance. Nevertheless, the aircraft
gun is still around today because no other gun cannon-sized gun can compete
with it for simplicity, reliability, and cost-effectiveness. The .50 BMG aircraft
is fully automatic, has a perforated barrel jacket that extends from the front
of the receiver to the muzzle, and can be setup to feed from either left or
right sides. The gun may be trigger fired or fired by a solenoid trigger.
Cyclic rate of the gun is 850 to 950 rounds/minute. The gun as two sets of forward
mounting holes: one set in the receiver for mounting on ground mounts and another
set provided by a trunnion adapter for mounting in aircraft. The aircraft
gun's barrel is 36 inches long and is Stellite and chrome lined for durability.
Weight of the basic AN/M2 aircraft gun is 64 pounds (without sights and
mount). Because aircraft guns recoil much harder than ground guns, the
oil buffer is filled with PLS oil. The AN/M2 aircraft gun is used as flexible
door guns by Army, Navy, and USMC helicopters. The AN/M2 aircraft fixed
gun is used in gun pods on various aircraft.
AN/M2 .50 BMG Air-cooled (heavy barrel,
ground)
The AN/M2 .50 BMG in its HB, or ground version,
is probably the most widely used heavy machinegun on the planet. It is
used on ships' mounts, small combatants' mounts, light armor mounts, heavy armor
mounts, soft-skinned vehicle mounts, ground mounts, and anti-aircraft mounts.
The gun can feed from either side, use either a manual or solenoid trigger,
and is distinguished by its short, stubby barrel support (barrel jacket).
The gun's cyclic rate is 450 to 550 rounds/minute. Weight of the gun is
82 pounds. The gun is 6 feet long and has a barrel 45 inches long that
weighs 28 pounds. The barrel is designed to act as a heat-sink when the
gun is fired on automatic. Maximum effective range is 2,000 yards.
Marine Corps sniper Carlos Hathcock recorded a 2,500 yard kill against the Viet
Cong using a sandbagged AN/M2HB and 8 power Unertl telescopic sight. The
big .50 is still the machinegun against which all other heavy machineguns are
measured. Many 20mm (and larger) guns have come and gone. Each has
been touted as a replacement for the .50. However, the .50 AN/M2HB is
still going strong and its 20mm replacements have been replaced.
R-1
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© 2002 Bob Stoner
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