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.  For  all  minor-  and  medium-caliber  projectiles, rotating bands are made of commercially pure copper or gilding   metal,   which   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  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 may be drilled and tapped in the center of the 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 a base fuze or tracer if desired. The edge formed by the side walls 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. Projectile  Types Projectiles are also classified by their tactical purpose. The following are descriptions of some of the common  projectile  types  (fig.  6-3). ANTIAIRCRAFT (AA).—Antiaircraft projectiles are  designed  for  use  against  aircraft;  they  have  no  base fuzes.  Otherwise,  they  are  substantially  the  same  as  the high-capacity  (HC)  projectiles  described  below. ANTIAIRCRAFT  COMMON  (AAC).—Antiair- craft common projectiles are dual-purpose projectiles combining most of the qualities of the AA-type with the strength  necessary  to  penetrate  mild-steel  plate (fig. 6-3, view A). However, AAC projectiles do not have the penetrating ability of common projectiles. The type of fuzing will depend on the use. Fuze threads are provided in the nose and in the base. AAC projectiles are normally equipped with a mechanical time fuze (MTF)  and  an  auxiliary  detonating  fuze  (ADF). Dual-purpose action is accomplished by a time setting for air burst or by setting MTFs on “safe” or for a time longer than flight-to-target to permit the base detonating fuze (BDF) (delay) to function for penetration. By substituting a point detonating fuze (PDF) for the MTF, you can convert these projectiles to high-capacity for surface  burst. CHEMICAL.—Chemical projectiles may be loaded with a toxic, harassing, or smoke-producing agent. Of the  smoke  agents,  white  phosphorous  (WP)  is  the  most frequently used. WP projectiles (fig. 6-3, view B) are designed to produce heavy smoke and, secondarily, an incendiary effect. The small WP containers are expelled and then scattered by a delayed action burster charge that is ignited by a black powder expelling charge. Other chemical  loads  are  dispersed  in  a  similar  manner. PUFF.—Puff projectiles (fig. 6-3, view C) are nonexplosive  projectiles  used  as  practice  (spotting) rounds. They are designed to produce dense smoke clouds  approximating  those  of  high-explosive  rounds. DRILL.—Drill projectiles are used by gun crews for loading drills and for testing ammunition hoists and other  ammunition-handling  equipment.  They  are  made of  economical,  but  suitable  metals,  and  are  designed  to simulate the loaded service projectile represented in size, form, and weight. They may be solid or hollow. If hollow, they may be filled with an inert material to bring them  to  the  desired  weight.  This  latter  type  is  closed  with a base or nose plug or both, as appropriate. DUMMY.—Dummy  projectiles  are  reproductions of projectiles that may be produced from a variety of materials for a number of purposes. Drill projectiles are dummy projectiles in that they are not to be fired from a gun; however, all dummy projectiles are not drill projectiles.  Dummy  projectiles  may  be  made  for display,  instruction,  or  special  tests. HIGH CAPACITY (HC).—High-capacity  pro- jectiles are designed for use against unarmored surface targets, shore installations, or personnel. They have a medium wall thickness and large explosive cavities. 6-4