Page:Encyclopædia Britannica, Ninth Edition, v. 11.djvu/320

Rh 304 G U K N E li Y BC EF ., clTFD ; tlien AC tan BAC, and CD - AC cosec ADC, so Putting the angle ADC (the ele- ., . BC tan BAG EF CD ^ cosec ADC = FD ration) = e, the angle BAC (the slope of the tangent sight) = 0, EF (the deflexion) =d, and DE (the range) = r, we have tan 6 = f cosec .-. r The action of the powder charge, the travel of the projectile along the bore, the rilling, and, speaking generally, what takes place inside a gun when fired, are matters specially connected with the designing and manufacture of ordnance, and are therefore treated under GUNMAKING. Projectiles. The requirements of modern artillery have necessitated many complications in the preparation and use of projectiles, which now vary greatly in their nature and in the purposes for which they are employed. A general description of the several kinds supplied to European armies will be found under AMMUNITION, and but few remarks will be required to connect them with the guns for which they are intended. Smooth-bored ordnance use solid round shot and case, common shell, and diaphragm, shrapnel shell. Solid shot are used against masonry, wooden shipping, and masses of men. They were at one time fired red hot at shipping. Roughly, the cube of the diameter in inches multiplied by 133 gives the weight of the shot in pounds, nooth- Case shot consist of iron balls packed in iron or tin cylin- )re drical cases. They are effective up to about 350 yards &quot;. against troops, boats, and rigging, and are especially suitable for flanking ditches. Common shell are completely filled with powder, and are burst in flight by time fuzes, or, on striking, by percussion fuzes. They are used against men in masses, buildings, works, and material generally. Diaphragm shrapnel shell contain a small bursting charge and a number of balls. They are fitted with a time fuze which explodes the charge when they near the object, so that the released ballets fly forward. They are very destruc tive against troops. In addition to the above projectiles, incendiary shells, called carcasses, filled with a violently burning composition, are thrown into villages and amongst shipping. Ground light balls cast among the enemy s working parties at night disclose their position. Parachute light balls contain a parachute tightly folded up, and a cup of illumining composition ; they are fired with a fuze timed to burst in the air, and they then remain suspended for a time, throwing a light down on the enemy s working parties. The great advantage of rifling was long recognized in small arms and sporting pieces before it was extended to ordnance. The first rifled arms threw bullets which, except for certain projections designed to fit the grooves of the barrel, were spherical. These guns surpassed smooth-bores in accuracy, but it was not till the introduction of elongated projectiles that a distinct gain in power was recognized. Rifled The gain in accuracy is due in great measure to the superior pro- correctness with which the ball is centred in the bore by lles- the action of the grooves, while the rotation imparted to it annuls or greatly lessens the disturbing effect of the pres sure of the air on surface inequalities, or of variations in the position of the centre of gravity. An elongated shot is also enabled to travel point first, or nearly so, and as the resistance of the air depends upon the area of the transverse section, a far greater weight can be given to the long than to the round shot without increasing this resistance. Thus, in addition to greater accuracy, rifling confers a flatter trajectory and greater penetration. The elongated form permits a head of the best shape, an increase in the con tents of the shell, and the use of fuzes which explode when the point strikes an object. The projectiles used with rifled guns are case shot, common shell, shrapnel shell, and Palliser shell. The case shot differ little from those made for smooth-bore ordnance. Common shell are generally from 2^ to 3 calibres in length. They are designed to Comrr contain as much powder as possible, consistently with shell, strength of wall to resist the shock of firing. Their effect Common shells are generally fuzed with percussion fu^es. They are effective for breaching, for setting fire to buildings, against troops if not much scattered, and especially against wooden or thinly plated vessels. The introduction of iron clad ships is almost entirely due to the terribly destructive fire of shells. Shrapnel shell are filled with bullets, and sin-ap have a bursting charge only sufficient to open the case and release the contents, which then fly forward with the I velocity possessed by the projectile before breaking up. The bullets and fragments very speedily lose this velocity after separation. It is therefore most important to judge j the range correctly and to form an accurate estimate of the practice, so that the result of each round may guide the aiming and timing of the next. When the shrapnel is burst in the air by a time fuze, it is exceedingly difficult to judge its precision by the puff of smoke. The splashes or puffs of dust of the bullets striking the ground should therefore be carefully looked for. When the shrapnel is burst on striking the ground by a percussion fuze, it is much easier to estimate the accuracy of the shooting, and it is common therefore to get the range by firing a round or two with percussion fuzes before setting the time fuzes. If the ground is hard and the distance of the enemy such that the shell strikes at but a small angle of descent, percussion fuzes generally burst the shrapnel better than time-fuzes, which, in their turn, have the advantage at long ranges and over soft ground. For field service time-fuzed shrapnel should be burst at from 50 to 100 jards in front of the object, and about 10 to 15 feet above the ground. The cone of dispersion of the bullets and fragments is con sidered to be so proportioned that the diameter at any point of the axis is one-third of the distance of that point from the burst or apex. To get satisfactory results from time fuzes it is necessary to have a gun which shoots with great regularity, a fuze ccmposition which burns evenly, and an accurate mode of setting the fuze. Of lute years improvements in powder and design of ordnance have rendered the velocities practically uniform. The fuze com position is somewhat liable to deterioration, but is tolerably satisfactory ; and a new fuze auger has just been introduced which can be set to any desired degree of accuracy. As the power of shrapnel! shell is entirely due to the velocity pos sessed by the bullets when freed from the envelope, it is of paramount importance in long-range firing that the shell should start with a high velocity and retain as much of it as possible. It is considered that with field guns the velocity of the projectile at the moment of bursting should not fall below 800 f. s., otherwise the contents will have a much diminished effect. The bullets themselves should retain a velocity of about 500 f. s. on striking to be thoroughly effective. With the more modern field guns the effective range of shrapnel extends up to about 3000 yards ; with heavy guns to 4000 or even 5000 yards. Palliser shells are made of a mixture of selected brands Armoi of iron, and are cast in moulds so constructed that the piercii metal of the head is in contact with iron and that of the s body with sand. The head is thus &quot; chilled,&quot; as the rapid carrying off of the heat by the iron mould causes the particles of the metal to dispose themselves rigidly, and confers intense hardness, which property is essential for the penetration of iron plates. The head is of the ogival shape, that being found most effective in combining strength with sharpness (fig. 18). It is a moot point whether projectiles of hardened steel are more effective than those of chilled iron against armour. Probably the steel can get through a
 * is almost entirely due to explosion ; velocity has little to
 * do with it beyond conferring range and penetration.