Causes of deviation of shot.
Very great irregularities occur in the paths described by projectiles fired from smooth-bored guns. It is a fact well known to all practical artillerists, that if a number of solid shot or any other projectile be fired from the same gun, with equal charges and elevations, and with gunpowder of the same quality, the gun carriage resting on a platform, and the piece being laid with the greatest care before each round, very few of the shot will range to the same distance; and moreover, the greater part will be found to deflect considerably (unless the range be very short) to the right or left of the line in which the gun is pointed.
Four causes of deviation.
The causes of these deviations may be stated as follows:—1st, Windage; 2nd, Rotation; 3rd, Wind; 4th, from Rotation of the Earth.
1st CAUSE, WINDAGE.
Action from windage.
Windage causes irregularity in the flight of a projectile, from the fact of the elastic gas acting in the first instance on its upper portion, and driving it against the bottom of the bore; the shot re-acts at the same time that it is impelled forward by the charge, and strikes the upper surface of the bore some distance down, and so on by a succession of rebounds, False direction.until it leaves the bore in an accidental direction, and with a rotatory motion, depending chiefly on the position of the last impact against the bore. Thus should the last impact of a (concentric) shot when fired from a gun be upon the right hand side of the bore, as represented, ([plate 23], fig. 5); the shot will have a tendency to deflect to the left in the direction. Gives rotation.While at the same time a rotation will be given to it in the direction indicated by the arrows.