Gun ammunition consists of a projectile and a propelling charge. In this section we will &scribe a typical projectile and the different types of projectiles, propelling charges, and fuzes currently in use.

Projectiles

The projectile is the component of ammunition that, when fired from a gun, carries out the tactical purpose of the weapon. While some types of projectiles are one piece, the majority of naval gun projectiles are assemblies of several components. AU the projectiles discussed (by classification) in this chapter have several common features, as described in the following paragraphs and as illustrated in figure 2-2.

OGIVE.- The ogive is the curved forward portion of a projectile. The curve is determined by a complex formula designed to give maximum range and accuracy. The shape of the ogive is generally expressed by stating its radius in terms of calibers. It maybe a combination of several arcs of different radii.

BOURRELET.- The bourrelet is a smooth, machined area that acts as a bearing to stabilize the projectile during its travel through the gun bore. Some projectiles have only one bourrelet (forward); the rotating band serves as the bearing surface in the rear. Still other projectiles have one bourrelet forward and

Figure 2-2.-external features of a typical gun projectile.

one or two aft, the after one being located adjacent to and either forward and/or aft of the rotating band. Bourrelets are painted to prevent rusting.

BODY.- The body is the main part of the projectile and contains the greatest mass of metal. It is made slightly smaller in diameter than the bourrelet and is given only a machine finish.

ROTATING BAND.- The rotating band is circular and made of commercially pure copper, copper alloy, or plastic seated in a scored cut in the after portion of the projectile body. In all minor and medium caliber projectiles, rotating bands are made of commercially pure copper or gilding metal that is 90 percent copper and 10 percent zinc. Major caliber projectile bands are of cupro-nickel alloy containing 2.5 percent nickel or nylon with a Micarta insert. As a projectile with a metallic band passes through the bore of the gun, a certain amount of copper will be wiped back on the rotating band and will form a skirt of copper on the after end of the band as the projectile leaves the muzzle of the gun. This process is known as fringing and is prevented by cutting grooves, called cannelures, in the band or by undercutting the lip on the after end of the band. These cuts provide space for the copper to accumulate. The primary functions of a rotating band are:

1. To seal the forward end of the gun chamber against the escape of the propellant gas around the projectile,

2. To engage the rifling in the gun bore and impart rotation to the projectile, and

3. To act as a rear bourrelet on those projectiles that do not have a rear bourrelet.

BASE.- The base is the after end of the projectile. A removable base plug is provided in projectiles that are loaded through this end. A fuze hole maybe drilled and tapped in the center of this base plug. Projectiles with large openings in the nose for loading through that end require no base plug. In such cases, however, the solid base of the projectile may be drilled in the center to receive abase fuze or tracer if desired The edge formed by the sidewalls and the base is usually broken slightly to give additional range. Some projectiles are tapered aft of the rotating band, a shape known as boat tailed. Projectiles with plastic bands may have full caliber boat tails for optimum aerodynamic shape.