Typical cartridge construction.
Depending on the job to be done, several types of projectiles can be fired from the caliber .50 machine gun. The method of firing the round is the same in all cases. The primer consists of a brass cup, a highly explosive primer charge, a shellacked paper disk to keep out moisture, and a brass anvil with a pointed end. The primer fits into a circular primer pocket in the base of the cartridge case. The front edge of the case is bent into a groove, or cannelure, in the side of the bullet to hold it in place. When the gun's firing pin dents the primer cup, the primer charge, squeezed between the cup and anvil, explodes. Flame flashes around the anvil and through a vent in the cartridge case, setting fire to the propelling charge, a quantity of black, smokeless powder loosely packed in the case. The propelling charge does not explode all at once, but burns steadily from back to front in a fraction of a second. Gases given off by this burning create the chamber pressure of about 50,000 pounds to a square inch. The case is forced against the sides of the chamber, and the projectile is blown forward out of the case and through the barrel. Types of Ammunition The types of ammunition used by aerial gunners can be identified by colors painted on the tips of the bullets. The chart on the next page shows the kinds of ammunition, and the use, identification, and construction of each type.

Ignition system detail.
TYPES OF AMMUNITION
Source: Aircrewmans Gunnery Manual, 1944
TYPEUSECOLOR OF TIPSHOW IT WORKS
Ball
(Cartridge, ball, caliber .50, M2)
Used against personnel
and light material targets.
Unpainted;
plain copper color.


A jacket of copper-colored gilding metal encloses the
steel core. A lead and antimony point filler fills up the space
between the point of the core and the jacket. When the projectile hits a target, the soft jacket smears, giving the
steel core a grip. The core penetrates the surface instead of being turned aside.

Armor-piercing (Cartridge, armor-
piercing, caliber
.50, M2)		 Used against armored aircraft and vehicles, concrete shelters, and other bullet-resisting targets. Black The projectile is the same as a ball cartridge, except that the core is made of a very hard tungsten chrome steel to give it greater penetrating power.
Tracer Cartridge,
tracer, caliber .50,
M2 or M 10		 Used for observing fire- it makes a streak of light easily seen at night, and usually visible in daylight. Red
Inside the gilding metal jacket is a slug of lead and antimony. Behind it is a pocket of tracer composition which is set afire by the propelling charge as the projectile leaves the cartridge case.
Incendiary
(Cartridge, incendiary, caliber .50, MI)		Used to set fire to explosive or very inflammable targets, like gasoline tanks and balloons.Light blue In the front of the jacket is an incendiary composition. It is sealed by plugs of an alloy which melts easily. As the bullet goes through the barrel, the heat melts the plugs. The incendiary composition is set on fire when the air touches it.
Dummy
(Cartridge, dummy,
caliber .50, M I or M2)		Used in training.Unpainted
(Hole in side of case)		A round with no priming charge and no propelling charge. A hole is drilled in the side of the case.
Armor-piercing incendiary
(Cartridge, armor-piercing incendiary, cal. .50, M8)		To set fire to armor plated inflammable objects, such as the gas tanks of fighter planes.Black, with a small blue tip on the nose. Similar in construction to armor-piercing projectile, except that there is incendiary compound behind the steel core.
.50 & .30 CALIBER M2 AIRCRAFT MACHINE GUNS
Source: Aircrewmans Gunnery Manual, 1944

DIFFERENCES
IN PERFORMANCE

CALIBER .50CALIBER .30
Weight64 pounds20 pounds
Rate of fire per minute750-850 rounds1,350 rounds (approx.)
Muzzle velocity (at 78 feet
from muzzle, with A.P. M2)		2,900 feet per sec.2,715 feet per sec.
Chamber pressure per sq. in.50,000 to 52,000 pounds48,000 to 50,000 pounds
Maximum range A.P. M27,200 yards 4,500 yards
Ground crewman load a P-51 Mustang
with .50 caliber linked ammunition.
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