caliber/case designation is on the first line. The
manufacturer symbol, interfix number, lot serial
number, and year of manufacture are on the second line.
The M103 case is loaded for use with all service
ammunition, and the M103B1 is used with the
M51A1B1/M51A2 dummy cartridges.
All M50-configured cartridges are loaded with
(double-base) ball spherical propellant WC 870 or 872.
M52A3B1 Electric Primer
The electric primer is used in all current M50
configurations. It consists of an open-ended brass cup
that contains a brass button insulated from the cup by a
plastic liner. The firing pin of the gun contacts this
button. The ignition charge (a conductive explosive
mixture) is in contact with the other side of the button,
and is retained by a paper disk and a metal support cup.
The electrically initiated primer ignites the propellant
NOTE: The primer explosive element is
sensitive to electromagnetic and electrostatic
All projectiles, except the HPT, have essentially the
same external configuration. The rotating band is a
copper alloy swaged into a circumferential groove near
the aft end of the steel body.
Fuze M505A3 Point-Detonating (PD)
The PD fuze (fig. 7-3) consists of a body assembly,
a rotor assembly, and a booster assembly. The fuze has
a delayed arming distance of 20 to 35 feet after it leaves
the muzzle of the gun. Before firing the HEI projectile,
the rotor and the firing pin are locked in position by the
rotor safety spring. (The rotor contains the detonator,
which is out of line with the firing pin.) Centrifugal
force causes the spring to open, allowing the rotor to
move in-line with the firing pin. The fuze functions
when the nose of the fuze is crushed against the target,
forcing the firing pin against the detonator. The
detonator, in turn, initiates the booster. The booster
detonates and initiates the projectile's explosive charge.
A tracer mix is direct-loaded into a cavity
machined in the base of the TP-T and HEI-T
projectiles. It is used in assembling the M220 and
M242 cartridges, respectively. The heat and pressure of
the propelling charge ignite the tracer. The tracer is
visible for about 1,280 yards of projectile flight.
M51A1B1/M51A2 DUMMY CARTRIDGES
Dummy cartridges are completely inert assemblies.
They are used for drill and testing the feeder assembly
of a weapon. The dummy cartridge is assembled with
cartridge case to simulate the service cartridge. The two
cartridges are the same except for a change to the
approximately 635 grains of inert material. This
material produces an average overall weight equal to
that of the other M50-configured ammunition.
M254 DUMMY CARTRIDGE
The M254 cartridge is made of plastic. It is an
alternate to the M51A1B1/M51A2 steel dummy
Figure 7-3.M505A3 point-detonating fuze (unarmed).