CHARACTERISTICS OF FIRE

F-17. The gunner’s or leader’s knowledge of the machine gun is not complete until he learns about the action and effect of the projectiles when fired. The following definitions will help the leader, gunner, and assistant gunner understand characteristics of fire of the platoon’s weapon’s squad machine guns.

LINE OF SIGHT

F-18. LOS is an imaginary line drawn from the firer’s eye through the sights to the point of aim.

BURST OF FIRE

F-19. A burst of fire is a number of successive rounds fired with the same elevation and point of aim when the trigger is held to the rear. The number of rounds in a burst can vary depending on the type of fire employed.

TRAJECTORY

F-20. Trajectory is the curved path of the projectile in its flight from the muzzle of the weapon to its impact. The major factors influencing trajectory are the velocity of the round, gravity, rotation of the round, and air resistance. As the range to the target increases, so does the curve of trajectory. (See figure F-7.)

MAXIMUM ORDINATE

F-21. Maximum ordinate is the highest point above the LOS the trajectory reaches between the muzzle of the weapon and base of target. It always occurs at a point about two-thirds of the distance from weapon to target and increases with range. Like trajectory, maximum ordinate increases as the range increases. (See figure F-7.)

CONE OF FIRE

F-22. The cone of fire is the pattern formed by the different trajectories in each burst as they travel downrange. Vibration of the weapon and variations in ammunition and atmospheric conditions all contribute to the trajectories making up the cone of fire. (See figure F-8.)

BEATEN ZONE

F-23. The beaten zone is the elliptical pattern formed when the rounds within the cone of fire strike the ground or target. The size and shape of the beaten zone change as a function of the range to and slope of the target, but is normally oval or cigar shaped and density of rounds decreases toward the edges. Gunners and AR should engage targets to take maximum effect of the beaten zone. The simplest way to do this is to aim at the center base of the target. Most rounds will not fall over the target, and falling short creates ricochets into the target. (See figure F-8.)

Effective Beaten Zone

F-24. Because of dispersion, only part of the beaten zone in which 85 percent of the rounds fall is considered the effective beaten zone.

Effect of Range on the Beaten Zone

F-25. As the range to the target increases, the beaten zone becomes shorter and wider. Conversely, as the range to the target decreases, the beaten zone becomes longer and narrower. (See table F-6.)

Effect of Slope on the Beaten Zone

F-26. The length of the beaten zone for given ranges varies according to the slope of the ground. On rising ground, the beaten zone becomes shorter but remains the same width. On ground sloping away from the gun, the beaten zone becomes longer but remains the same width.

DANGER SPACE

F-27. This is the space between the muzzle of the weapon and target where trajectory does not rise above 1.8 meters (the average height of a standing Soldier) including the beaten zone. Gunners should consider the danger space of weapons when planning overhead fires.

SURFACE DANGER ZONE

F-28. Surface danger zones were developed for each weapon and are defined as the area in front, back, or side of the muzzle of the weapon providing a danger to friendly forces when the weapon is fired. The surface danger zone is not just the area comprising the cone of fire as it moves downrange. It also involves the possible impact area on both sides of the gun target line and possible dispersion of materiel caused by the strike of the rounds, the possible ricochet area, and areas to the rear adversely affected by the effects of firing the weapon. (See figure F-9.)

F-29. Surface danger zones were developed primarily for ranges and must be complied with when training, but they also should be complied with in combat when possible to minimize risk to friendly forces. (Refer to DA Pamphlet 385-63 for more information.)