Frequent changes of sight not only cause a loss of time, but they also multiply chances of error in sight-setting. Changes in sight-setting against advancing infantry should not be less than 200 yards at a time, that is to say, when the enemy has passed through the zone of effective fire, the sight should be lowered 200 yards and the operation repeated until the battle-sight zone is reached, when the rear-sight leaf is thrown down and no other sight manipulation is made.
Against skirmish lines advancing by rushes, the sight-setting should not be changed during a rush, but it should be done at the halts, so that the greater vulnerability of the targets presented during the rush may be taken advantage of.
Against retreating infantry, use the estimated range, and when the target appears to have passed beyond the zone of effective fire, add 200 yards to the sight-setting.
Against attacking cavalry, due to the rapidity of the advance, there will not usually be time for sight manipulation other than throwing down the rear-sight leaf, so that the battle should be resorted to at all ranges.
In firing at a target moving across the line of fire it is desirable, on account of the confusion caused thereby, to hit the head of the column. It is necessary, therefore, to hold to the front a distance sufficient to allow for the time of flight and the rate of march. This will be accomplished by the observance of the following rough rules:
1. Against infantry, hold against the head of the marching column;
2. Against cavalry at a trot, hold to the front 1 yard for every 100 yards of range; and at a gallop, 2 yards for every 100 yards of range.
[1433]. Night firing. In night firing it is almost impossible to adjust the fire by ordinary means.
In night attacks the purpose of the offensive is to gain rapidly and quietly a position where the issue may be decided in a hand to hand encounter, or a position from which the superiority of fire may be gained at daylight. For the offensive, therefore, fire action is a subordinate consideration.
On the defensive, when a night attack is apprehended, preparations should be made to sweep with fire the ground immediately in front over which the assailant must advance.