The technique of fire is the application and control of the combined fire of a fire unit. The rest of this chapter concerns the technique of fire for rifle and machine gun units.

FIRE CHARACTERISTICS

The fire of rifles and machine guns has the following characteristics: trajectory, danger space, burst of fire, dispersion, shot patterns, and beaten zone.

The TRAJECTORY is the curved path of the bullet in its flight through the air. Trajectory is influenced by three forces: velocity of the projectile, gravity, and air resistance. The farther the bullet travels, the greater the curvature of its path becomes. The highest point on the trajectory (called the maximum ordinate) is a point at

Figure 3-57.-Projector of 7.62-mm ammunition showing maximum ordinate (H) of trajectory.

Figure 3-58.-Danger space at 1,000-yard range.

Figure 3-59.-Cone of dispersion, or cone of fire.

approximately two-thirds of the range from the weapon to the target (fig. 3-57). DANGER SPACE is the area between the weapon and the point of impact in which the bullet does not rise above the average height of a man (presumed to be 68 inches). At ranges up to 750 yards, a rifle bullet fired over level or uniformly sloping ground does not rise above this height; therefore, for such ranges, the danger space is continuous. At ranges greater than 750 yards, a portion of the trajectory is above this height; therefore, the danger space is not continuous but exists for a variable distance in front of the muzzle and in front of the point of impact. In the latter case, the danger space begins again when the bullet comes within 68 inches of the ground. The length of the two danger space zones is dependent upon the range, as shown in figure 3-58. A number of shots fired automatically with a single pressure on the trigger is called a BURST OF FIRE. For normal ground targets, the number of rounds in a burst is usually from four to ten.

When several bullets are fired from a rifle or machine gun held in a fixed position, there is a slight variation in the trajectories. The causes of these differences are in the powder charge, the weight of the bullet, atmospheric and wind conditions, and vibration of the weapon. These variations are known as DISPERSION. The several dispersions, plotted in profile, form a cone with its apex to the muzzle of the weapon; this is known as the cone of dispersion, or the cone of fire (fig. 3-59).

The impact pattern of the cone of dispersion on a vertical target (which would be oval in shape) is called the VERTICAL SHOT PATTERN. (See fig. 3-60.) The

Figure 3-61.-Horizontal shot patterns at various ranges.

Figure 3-62.-Effect of ground slopes on beaten zone.

impact pattern on a horizontal target, which would be a long, narrow ellipse, is known as the HORIZONTAL SHOT PATTERN or BEATEN ZONE. (See fig. 3-61.) The BEATEN ZONE is the area of the ground the bullets strike. The size and shape of the beaten zone depend upon the range and slope of the ground, as shown in figure 3-62.