5. The Beaten Zone.—(i) The area of ground beaten by a cone of fire is termed the “beaten zone.” It is regarded as a plane surface. [Fig. 6] illustrates this zone together with the additional space which would have to be taken into account in reckoning the dangerous space of the cone of fire in consequence of the height of the objective.
(ii) Depth of Beaten Zone.—The depth of the beaten zone at short ranges need not be considered on account of the flatness of the trajectory, which insures that practically its whole extent from the firers to the target is swept by bullets. The depth of the beaten zone at various ranges with the Mark VI and Mark VII ammunition is as follows:
| Distance. | Depth of Beaten Zone. | |
|---|---|---|
| Mark VI. | Mark VII. | |
| 500yards | 220yards | 300yards |
| 1,000” | 120” | 180” |
| 1,500” | 100” | 120” |
(iii) It will be seen that up to 1,500 yards—when the ground is parallel to the line of sight—the depth of the beaten zone decreases with the range, on account of the increased angle of descent of the bullets. This shrinkage of the beaten zone does not of itself increase fire effect by the closer grouping of bullets, owing to the increased steepness of the angle of descent, which decreases dangerous space.
(iv) Beyond 1,500 yards it will be found that the depth of the beaten zone tends to increase in consequence of the influence of atmospheric conditions on the flight of the bullet, the increased effects of errors in aiming, and faults in the rifle and ammunition—all of which combine to increase the dispersion of fire. This increased dispersion does not of itself increase fire effect owing again to the greatly increased steepness of the angle of descent at longer ranges, which results in a correspondingly great decrease in dangerous space.
(v) Lateral Dispersion.—On the other hand, owing to faults in aiming, comparative invisibility of the target, inaccuracies in the rifle and ammunition, and atmospheric influences, the lateral dispersion of a cone of fire increases as the range becomes greater. With Mark VI ammunition, the dispersion of the best 75 per cent. of shots fired may be taken as 7 feet by 220 yards at 500 yards, 14 feet by 120 yards at 1,000 yards, and 22 feet by 100 yards at 1,500 yards.
6. Nucleus of Cone of Fire.—It is found that the bullets in a cone of fire are not dispersed evenly over the surface of the beaten zone. It is found that they are grouped in such a way that the majority of the bullets fall in the general direction of the line of fire, that the density of the grouping decreases progressively from the centre to the extreme limits of the beaten zone, and that the bullets are collected most thickly near the point for which the sights were set. This dense grouping is usually termed the nucleus of the cone of fire, and is regarded for purposes of comparison as including the best 50 shots per cent.
7. Zone of Effective Fire.—The area of ground beaten by the best 75 shots per cent. fired is termed the zone of effective fire, for it has been found by experiment that useful results in battle can only be looked for when the target is within these limits.
Section 13.—Searching.
1. Definition of Searching.—Searching is the term applied to collective fire when the depth of its dispersion over a beaten zone is increased by the use of combined sights as described in para. 4 of this section.