Effect on Masonry.—The effect of a projectile against masonry is to form a truncated conical hole, terminated by another of a cylindrical form. The material in front of and around the projectile is broken and shattered, and the end of the cylindrical hole even reduced to powder. The exterior opening varies from four to five times the diameter of the projectile, and the depth varies with the size and density of the projectile, and its velocity. When a projectile strikes against a surface of oak, as the side of a ship, it will not stick if the angle of incidence be less than 15°, and if it do not penetrate to a depth nearly equal to its diameter. Solid cast-iron shot break against granite, but not against freestone or brick. Shells are broken into small fragments against each of these materials.
Breaching.—Formerly stone projectiles were much used for breaching, but from the want of sufficient hardness in these projectiles, the besiegers were forced to commence battering at the top of the wall where the least resistance was offered, and gradually to lower the shot until the breach reached the wrecks already formed at the base of the wall. Iron projectiles superseded stone, and then more rapid modes of effecting a practicable breach were suggested. The easiest manner of making the cut is to direct the shots upon the same line, and form a series of holes a little greater than a diameter apart, and then to fire a second series of shots, directed at the intervals between the first, and so on, until an opening is made completely through the wall. If the portion of the wall between the vertical cuts should not be overthrown by the pressure of the earth behind, it must be detached by a few volleys of solid shot, fired at its centre.
Breaching with Rifle-cannon.—The foregoing has reference particularly to breaching masonry with smooth-bored guns. The same principle is applicable to rifled guns, the only difference being that, from their superior penetration and accuracy, the latter are effective at much longer distances. The most destructive projectile against masonry is the elongated percussion shell.
Effect of Bullets.—From experiments made in Denmark, the following relations were found between the penetration of a bullet in pine and its effects on the body of a living horse, viz.: 1st. When the force of the bullet is sufficient to penetrate 0.31 inch into pine, it is only sufficient to produce a slight contusion of the skin. 2d. When the force of penetration is equal to 0.63 inch, the wound begins to be dangerous, but does not disable. 3d. When the force of penetration is equal to 1.2 inch, the wound is very dangerous. A plate of wrought iron three-sixteenths of an inch thick, is sufficient to resist a rifle-musket bullet at distances varying from 20 to 200 yards. Iron of thickness, however, will not resist bullets of the present day. That a rope mantlet may give full protection against rifle-musket bullets, it should be composed of five layers (three vertical and two horizontal) of 41⁄2-inch rope.
Projection. In mathematics, the action of giving a projectile its motion. It is also used to signify a scheme, plan, or delineation.
Proking-spit. A large Spanish rapier.
Prolongation. An extension of leave of absence, or a continuation of service.
Prolongation of the Line. Is effected by parallel movements at the right or left of any given number of men on a front division.
Prolonge. See [Implements].
Prolonge-hooks. See [Ordnance, Carriages for, Nomenclature of Artillery Carriage].