(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. =2. When Collective Fire is Effective.=--As already stated, collective fire will not as a rule produce results commensurate with the amount of ammunition expended, or fulfil the purpose for which it is used unless the target is included within the area beaten by 75 per cent. of the bullets directed upon it--that is to say, unless it lies in the zone of effective fire (Fig. 7, C). [Illustration: A B C D Nucleus Error Target on exceeding half included Combined Target depth of in Sights Effective Zone Effective Zone =Fig. 7.= DIAGRAMS ILLUSTRATING THE DISPERSION IN DEPTH OF CONCENTRATED COLLECTIVE FIRE AT 1,500 YARDS AND ITS DISTRIBUTION IN DEPTH BY THE USE OF COMBINED SIGHTS.] =3. When Collective Fire is not Effective.=--If an error in sighting is made which would result in the nucleus of the cone of fire striking at a distance short of or beyond the target which is equal to _half the depth measurement of the zone of effective fire_, the target will not be included in this zone, and the _fire will be ineffective_ (Fig. 7, B).