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3B5. Case ammunition

Gun ammunition which has its propellent charge in a metal case or cartridge instead of a bag is called case ammunition.

(The term “cartridge” may also be applied to a complete round of small-arms ammunition.) Both semifixed and fixed ammunition are of this type.

The factor that determines whether ammunition for a certain gun will be fixed or semifixed is the size and weight of a unit which can be handled by one man.

Although mechanical improvements in loading tend to minimize this weight factor at the gun, it must still be considered in the supplying of reloads from handling rooms below.

The primer in case ammunition is inserted in the base of the case at the ammunition depot and is not removed or changed aboard ship.

The designs of various sizes of case ammunition are similar, as may be seen from study of figure 3B3 and figure 3B4.
The preparation of the case assemblies is comparable up to the point at which the mouth of a case is sealed.

In fixed ammunition the projectile is the seal; a mouth plug is used in semifixed charges.

There are four steps in the assembly of case ammunition: (1) priming, (2) loading the propellant, (3) fitting a wad and sometimes a distance piece, and (4) inserting the projectile or mouth plug.

In priming, the primer used is either screwed (40-mm, and larger) or force-fitted (smaller cartridge ammunition) into the base of the case.

The desired weight of smokeless-powder grains is then dumped loosely into the case.

In 40-mm and larger guns, a cardboard disc, or wad, is forced into the case and a distance piece, if one is needed, placed on top.

The mouth of a semifixed case is then sealed by the insertion of a mouth plug as illustrated by the 5”/38 case in figure 3B4.

In fixed ammunition, the mouth of the case is sealed by forcing in the base of the projectile until the rear of the rotating band makes contact with the case.

A distance piece is made from a rectangular cardboard sheet, folded into a triangular shape and cut to the length necessary to fit the assembly, so that when placed between the wad and the case closure or mouth plug, it will hold the propellant firmly in place.

A case mouth plug may be of cork, plastic, or cardboard and must be of sufficient strength to keep the contents of the case from spilling out under any conditions of handling or loading.

In small-caliber ammunition, the fitting of wads and distance pieces may not be necessary if the propellant fills the case.

The cartridge case itself is a hollow cylinder with either a straight or a bottle neck.

The base has a rim around its circumference to facilitate extraction of the empty case from the gun.

The empty cases can be reused several times after being reprocessed at an ammunition factory.

3B6. Case ammunition containers

Since leaks may exist around the primer and the projectile or mouth plug, the case cannot always be relied upon to remain airtight.

Therefore like powder bags, case ammunition is transported and stowed in containers which provide air- and water-tightness.

There are several types of tanks and boxes in service, and no attempts will be made here to describe them in detail. It is sufficient to state that regardless of varying design, the container must, above all, provide proper storage for smokeless powder. In addition, the container should be strong but not unduly heavy, should handle easily, and should open quickly. Metal tanks made of aluminum most nearly conform to these requirements, and tanks in current use are of either aluminum or steel construction. Metal tanks are also advantageous in that they provide good storage in ready service racks on deck, or in ammunition-handling rooms not equipped to provide the best storage conditions.

C. Primers

3C1. General

A primer is a device used to initiate a flame for the ultimate purpose of igniting a charge of propellant. In bag ammunition this flame is applied to the ignition pad (the auxiliary ignition charge) in the base of the powder bag, which in turn ignites the smokeless powder. In case ammunition the ignition charge is incorporated into the primer tube. Since the ignition charge incorporated in the bag can be proportional in size to the charge, the primers are the same for bag guns of all sizes. However, primers of different sizes must be used in cases of different sizes so that the amount of black powder in the primer may be proportional to the amount of propellant.

3C2. Types and classes of primers

Primers are divided into two types, depending on how they are used in the gun:

(1) case

(2) lock.

They are also divided into three classes, depending upon the method of firing:

(1) percussion

(2) electric

(3) combination.

Percussion primers are fired by the mechanical impact of a firing pin.

Electric primers are fired by passing a current through a resistance filament surrounded by an initiating mixture.

Combination primers may be fired by either of these methods.

The current trend is toward the use of electric primers only, in case guns of 3-inch and larger caliber.

Except for 5-inch mounts and older 6-inch turrets, case combination primers are used only in short cartridge cases for clearing the barrel after a failure to fire electrically.

The following service primers are in current use:

1. Case percussion primer.
2. Case electric primer.
3. Case combination primer.
4. Lock combination primer.
3C3. Case percussion primer

This type is used in light and heavy machine guns such as the 20- and 40-mm. In ammunition for the smaller guns, which has a relatively small amount of propellant, the primer consists only of a cap, an anvil, and a percussion-sensitive mixture. The composition of the mixture varies with the amount of heat, flame, and sensitivity desired. In operation, the firing pin strikes the inverted cup which holds the primer cap. This indents the cup, forcing the cap against the anvil and exploding the pellet of initiating mixture. The resulting flame ignites the propellant. Where greater energy is required to ignite the propellant, the primer includes a black-powder charge which is ignited by the percussion cap. The 40-mm gun uses a primer of this type.

See figure 3C1.
3C4. Case electric primer

Case electric primers (fig. 3C2) are used for the newer 3-, 5-, 6-, and 8-inch guns. These primers contain an electric ignition element which consists of two resistance filaments connected in parallel and surrounded by an explosive mixture, and a small black-powder primer charge. An electric current heats the filaments, which then ignite the explosive mixture. Flame from the initiating mixture ignites the black-powder primer charge, which in turn ignites the main black-powder charge of the primer.
3C5. Case combination primer

This type of primer is used in the 5”/38 caliber and the older 5”/54 and 6”/47 caliber guns. It is also used in clearing charges for all case guns of 3-inch caliber and larger. These primers can be fired, as indicated by their name, either by percussion or electrically. Electrical firing is considered the primary method; the percussion feature is a standby for use in the event that electric firing fails. The percussion element is similar to that of the case percussion primer, except that the firing pin strikes a plunger which in turn explodes the cap against the anvil. The flames produced by the primer cap act directly upon the powder in the electric ignition cup. See figure 3C3.
The electric element consists of a high-resistance wire wrapped in a wisp of guncotton and contained in a mixture of pulverized guncotton and fine black powder in the ignition cup. This wire is connected at one end to the percussion plunger group, which is insulated from the primer stock. The other end of the wire is grounded through the primer stock and the cartridge case to the metal of the gun. In firing the gun an electric current is passed through the firing pin to the plunger; this heats the bridge wire, igniting the wisp of guncotton. The mixture in the ignition cup is ignited and in turn fires the black-powder primer charge. The primer charge is surrounded by the larger black-powder ignition charge and placed in an outer perforated tube, which amplifies the heat and flame sufficiently to surround the propellent charge.

3C6. Lock combination primer

The same type and size of primer (fig. 3C4) is used in all United States Navy bag guns. A primer is placed by hand in the firing lock of the gun each time the gun is loaded. There is no ignition charge in the primer, as one is included in the assembled powder bag. The percussion and electric features of the lock combination primer are the same as those of the case combination primer.