CHAPTER 7 - AMMUNITION LOADING

Aircraft gun ammunition is developed for specific types of aircraft-mounted guns. The M61A1/A2 uses M50 series 20-mm ammunition. The M50 series consists of various types of cartridges developed for specific applications, including test cartridges, dummy cartridges, target practice, target practice tracer, armor piercing incendiary, high-explosive incendiary, and semi-armor piercing, high-explosive incendiary. Blank and dummy rounds are also used for practice and maintenance.

The M50 series 20-mm ammunition is loaded into the M6lA1 gun through the linkless ammunition loading system (LALS). The LALS transports rounds from the transporter to the aircraft system, and simultaneously transports spent cases and cleared rounds from the aircraft system to the transporter.

AIRCRAFT GUN AMMUNITION

LEARNING OBJECTIVE: Recognize the 20-mm M50 aircraft gun ammunition configuration. Identify M50 20-mm gun cartridges and recognize their uses.

M50 configuration ammunition (fig. 7-1) for the M61A1 Navy aircraft gun is issued in the form of cartridges (rounds). A complete service cartridge assembly consists of a cartridge case, electric primer, propellant, projectile, and fuze. All service cartridges have matched ballistics and are electrically primed.

CLASSIFICATION

The M50 configuration ammunition currently issued is classified as follows:

Figure 7-1.-M50 configuration cartridge.

1. Dummy Cartridge M51A1B1, M51A2 (steel), or M254 (plastic)

2. High-Pressure Test Cartridge, M54A1 (HPT,)

3. Target Practice Cartridge, M55A2 (TP)

4. High-Explosive Incendiary Cartridge, M56A3 (HEI)

5. Target Practice-Tracer Cartridge, M220 (TP-T)

6. High-Explosive Incendiary-Tracer Cartridge, M242 (HEI-T)

CARTRIDGE COMPONENTS, GENERAL DESCRIPTION

The cartridge components for M50-configured ammunition as used in a complete round are discussed in the following paragraphs.

Cartridge Case

The M103 (brass) and the M103B1 (steel) cartridge cases (fig. 7-2) are marked longitudinally. The 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

Figure 7-2.-M103 (brass) and M103B1 (steel) cartridge cases. 7-1

ammunition, and the M103B1 is used with the M51A1B1/M51A2 dummy cartridges.

Propellant

All M50-configured cartridges are loaded with (double-base) ball spherical propellant.

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 charge.

NOTE: The primer explosive element is sensitive to electromagnetic and electrostatic energy.

Projectiles

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.

Tracer

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,

Figure 7-3.-M505A3 point-detonating fuze (unarmed).

respectively. The tracer is ignited by the heat and pressure of the propelling charge. 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 the M51A1B1/M51A2 projectile and M103B1 cartridge case to simulate the service cartridge. The two cartridges are the same except for a change to the annulus/primer pocket. The cartridge contains approximately 635 grains of inert material. This material produces an average overall weight equal to that of the other M50-configured ammunition.