Part 106

_Armstrong Projectile._--But one kind of projectile is used in the Armstrong breech-loading guns for the field service, and this is so constructed as to act as a shot, shell, or case-shot at pleasure. It consists of a very thin cast-iron shell, inclosing 42 segment-shaped pieces of cast iron built up so as to form a cylindrical cavity in the centre, which contains the bursting charge and the concussion-fuze. The exterior of the shell is thinly coated with lead, which is applied by placing the shell in a mold and pouring it in a melted state. The lead is also allowed to percolate among the segments, so as to fill up the interstices, the central cavity being kept open by the insertion of a steel core. In this state the projectile is so compact that it may be fired without injury, while its resistance to a bursting charge is so small that less than one ounce of powder is required to burst it. When the projectile is to be tired as a shot, it requires no preparation; but the expediency of using it otherwise than as a shell is doubted. To make it available as a shell, the bursting tube, the concussion- and time-fuzes, are all to be inserted; the bursting tube entering first and the time-fuze being screwed in at the apex. If the time-fuze be correctly adjusted, the shell will burst when it reaches within a few yards of the object; or failing in this, it will burst by the concussion-fuze when it strikes the object, or grazes the ground near it. If it be required to act as a canister-shot upon an enemy close to the gun, the regulation of the time-fuze must be turned to the zero of the scale, and then the shell will burst on leaving the gun. The Armstrong projectiles for the muzzle-loading guns have rows of brass or copper studs projecting from their sides to tit into the grooves of the gun, which are constructed on the _shunt_ principle. The projectile is made of wrought iron, or low steel, with very thick sides. There is no fuze, the explosion resulting from the heat generated by the impact, and the crushing in of the thin cap which closes the mouth of the powder-chamber. The sides and bottom of the shell being thick enough to resist crushing by the impact, and also to resist the explosive force of the bursting charge, its effect will, after penetration, be expended on the backing of the armor, or the decks which the armor is intended to screen. Such projectiles are called “blind shells.”

_Blakely Projectile._--Capt. Blakely’s projectile has an expanding cap attached to its base by means of a single tap-bolt in the centre. It is prevented from turning by radial grooves cast on the surface of the bottom of the projectile, into which the cup is pressed by the charge. The angle between the curved sides of the cup and the bottom of the projectile is filled with a lubricating material. On the forward part of the body are soft metal studs, more numerous than the grooves of the bore of the piece, that some of them may always form a bearing surface for the projectile against the lands. The driving sides of the grooves are deeper than the others.

_Dyer Projectile._--The Dyer projectile is composed of a cast-iron body, and a soft metal expanding cup, attached to its base. The adhesion of the cup is effected by tinning the bottom of the projectile, and then casting the cup on to it. The cup is composed of an alloy of lead, tin, and copper, in certain proportions. This projectile, as improved by Mr. Taylor at the Washington Arsenal, gives good results for even as large a caliber as 12 inches.

_French Projectile._--The projectile used in the French field service is made of cast iron, and has 12 zinc studs on its sides, arranged in pairs, so as to fit the 6 grooves of the gun. For the larger cannon projectiles, but 3 studs are used, and these are cast on the projectile, nearly opposite to its centre of gravity; the bearing sides of the studs are faced with white metal to diminish friction against the grooves of the bore. The shape of the grooves is such as to centre the projectile. The latter projectile is used with increasing, the former with grooves of uniform twist. Russian, Austrian, and Spanish artillery projectiles belong to the studded, or button class, but differ from each other in the details of their construction.

_Hotchkiss Projectile._--The Hotchkiss projectile is composed of three parts: the body, the expanding ring of lead, and the cast-iron cup. The action of the charge is to crowd the cup against the soft metal ring, thereby expanding it into the rifling of the gun. The time-fuze projectile has deep longitudinal grooves cut on its sides to allow the flame to pass over and ignite the fuze. The last rifle projectile submitted by Mr. Hotchkiss has an expanding cup of brass attached to its base in a peculiar manner. The cup is divided into four parts by thin projections on the base of the projectile. This arrangement is intended to facilitate the expansion of the cup and to allow the flame to pass over to ignite the fuze.

_James Projectile._--The expanding part of the James projectile consists of a hollow formed in the base of the projectile, and eight radial openings, which extend from this hollow to the surface for the passage of the flame of the charge, which presses against and expands into the grooves of the bore, an envelope or patch, composed of paper, canvas, and lead. In a later pattern of this projectile, the internal cavity and radial openings are omitted, and the outside is furrowed with longitudinal grooves which increase in depth towards the base of the projectile, forming inclined planes, up which the outer covering of lead and canvas is moved by the force of the charge and expanded into the rifling of the piece.

The first projectile used in Parrott guns was invented by Dr. Reed of Alabama, in 1856 or 1857, and was made at Parrott’s foundry. It consisted of a soft wrought-iron cup, slightly swedged to fit the grooves, upon which was cast the body of the shot.

_Palliser Projectile._--This is the most formidable armor-piercing projectile in use. It owes its efficiency to the material used,--chilled cast iron. In the later forms the head only is chilled, the body being cast in sand. Both shot and shell are cast with a core. The shell is “blind.” The curve of the ogival head is struck with a radius of one and one-half times the diameter of the projectile.

_Parrott Projectile._--Capt. Parrott’s projectile, as now made, is composed of a cast-iron body with a brass ring cast into a rabbet formed around its base. The flame presses against the bottom of the ring and underneath it so as to expand it into the grooves of the gun. To prevent the ring from turning in the rabbet, the latter is recessed at several points of its circumference. _Parrott’s incendiary shell_ has two compartments formed by a partition at right angles to its length. The lower and larger space is filled with a burning composition, the upper one is filled with a bursting charge of powder, which is fired by a time- or concussion-fuze. The burning composition is introduced through a hole in the bottom of the shell, which is stopped up with a screw-plug.

_Sawyer Projectile._--The Sawyer projectile has upon its sides six rectangular flanges or ribs to fit into corresponding grooves of the bore. To soften the contact with the surface of the bore, the entire surface of the projectile is covered with a coating of lead and brass-foil. The soft metal at the corner of the base is made thicker than at the sides to admit of being expanded into the grooves, and thereby closing the windage. In the latest pattern of Sawyer projectiles, the flanges are omitted, and the projectiles are made to take the grooves by the expansion of the soft metal at the base, which is peculiarly shaped for this purpose.

_Schenkle Projectile._--Schenkle’s projectile is composed of a cast-iron body, the posterior portion of which is a cone. The expanding portion is a _papier-maché_ sabot or ring, which is expanded into the rifling of the bore by being forced on to the cone by the action of the charge. On issuing from the bore the wad is blown to pieces, leaving the projectile unencumbered in its flight. A great difficulty has been found in practice in always getting a proper quality of material for the sabot, and in consequence, these projectiles have not been found to be reliable.

_Scott Projectile._--The shell devised by Commander Scott of the British navy, for firing molten iron, has three ribs cast upon it, which fit grooves so constructed as to centre it in the bore of the gun when fired. The interior of this shell is lined with loam to prevent the heat of the charge from penetrating through to the bursting charge. It is supposed to be broken and its contents diffused on striking the object.

_Whitworth Projectile._--The cross-section of the bore of the Whitworth gun is a hexagon with the corners slightly rounded. The projectile is first formed so that its cross-section is a circle, and its sides taper towards both ends. The middle portion is then carefully planed off to fit the bore of the gun. The Whitworth blind shell for firing against armor-plates, is made of tempered steel, and each end is closed with a screw. To prevent the heat of impact from acting too soon on the bursting charge, it is surrounded by one or more thicknesses of flannel. A 7-inch shell of this kind has been found to have sufficient strength and stiffness to penetrate 5 inches of wrought iron before bursting.

_Confederate Projectiles._--The rifle projectiles used by the Confederates in the late war belonged, with a few exceptions, to the expanding class. Besides the above there are three kinds of projectiles much used in the U. S. service, viz.:

_Absterdam Projectile._--The best form is cast in a single piece, and has an expanding ring of brass which projects three-eighths of an inch beyond the base of the projectile.

_Eureka Projectile._--Consists of a cast-iron body in one piece, with a brass sabot; the sabot is an annular disk intended to move on the frustum of a cone with an expanding cup in rear to take the grooves.

_Ordnance Projectile._--Consists of a cast-iron body, with a sabot composed of an alloy of lead and tin, which is cast on the base of the projectile, and is held in position by undercuts and dovetails, the action of the charge being to force the sabot on the cast-iron body and to make it take the grooves.

Projectiles of special construction were formerly much used for particular purposes, as:

_Bar-shot_, which consisted of two hemispheres or spheres connected by a bar of iron either rigidly or in such a manner as to traverse its length; these were useful in cutting the masts and rigging of ships.

_Chain-shot._--This differed from bar-shot only in the mode of connection, which was a chain instead of a bar.

_Chain-ball._--To arrest the motion of rotation of an oblong projectile thrown under high angles, and with a moderate velocity, it has been proposed to attach a light body to its posterior portion by means of a cord, or chain, which will offer a resistance to the flight of the projectile, and cause it to move with its point foremost.

_Nail-ball._--A round projectile, having a projecting pin to prevent it from turning in the bore of the piece.

_Grooved Ball._--An oblong projectile, having spiral grooves cut along its base, by means of which the action of the charge produces rotation about the longer axis of the projectile. Sometimes these grooves are cut in the forward part of the projectile for the action of the air. Neither of these plans has succeeded in practice.

_Bullets._--A bullet is a leaden projectile discharged from a musket, fowling-piece, pistol, or similar weapon.

_Spherical Bullets._--When smooth-bore muskets alone were used the bullets were chiefly spherical in form and made by casting; at present, however, spherical bullets are manufactured by a compressing machine invented by Mr. George Napier. They are denominated by the number contained in a pound. In consequence of the great improvements that have been made of late in small-arms, the spherical bullet is now very little employed for military purposes, its use being chiefly confined to case-shot.

_Oblong Bullets._--Are denominated by their diameter and weight. About 1600, when rifles began to be used as a military weapon, spherical bullets were fired; in the early part of the 18th century, however, it was found that good results could be obtained by the use of oblong projectiles of elliptical form. The great difficulty, however, of loading the rifle, which was ordinarily accomplished by the blows of a mallet on a stout iron ramrod, prevented it from being generally used in regular warfare. The foregoing plan was afterwards improved by making the projectile a little smaller than the bore, and wrapping it with a patch of cloth greased to diminish the friction in loading. The improvements which have been made in the last thirty years have entirely overcome this difficulty, and rifles are now almost universally employed, although until 1855 the mass of the American infantry was armed with smooth-bored muskets. The first person to overcome the difficulty of loading rifles was M. Delavigne, an officer of the French infantry. His plan, proposed in 1827, was to make the projectile small enough to enter the bore easily and to attach it to a sabot, which, when in position, rested upon the shoulder of a cylindrical chamber formed at the bottom of the bore to contain the powder. In this position the projectile was struck two or three times with the ramrod, which expanded the lead into the grooves of the barrel. The method of Delavigne was afterwards improved by Thouvenin and Minié, both officers of the French service. The projectiles suggested by them were elongated in form and the metal of the projectile was forced into the grooves of the rifling by means of a plug or cup driven into the base of the projectile, which was cast hollow for that purpose. The cup used in the Minié bullet wits made of sheet-iron. Mr. Greener of England appears to have been the first person to utilize this expanding or dilating action. Various other bullets have been invented, of greater or less usefulness, as the Whitworth, Pritchett or Enfield, and those used in the French, Austrian, and Swiss services. In the British service, the Enfield bullet is employed; this has a perfectly smooth exterior, and a conical boxwood plug inserted into a cavity at the base; they are made by machinery which draws in a coil of leaden rod, unwinds it, cuts it to the required length, stamps out the bullets with steel dies, drops them into boxes, and conveys them away.

_United States Bullets._--The bullets used in the U. S. service are of two kinds, one for the rifle and carbine ball-cartridge weighing 405 grains, the other for the revolver cartridge weighing 230 grains. The metal used is an alloy of 16 parts of lead and 1 part of tin. The bullet in shape is a cylinder surmounted by a conical frustum terminating in a spherical segment. It has three rectangular cannelures which contain the lubricant. This latter is protected by the case which covers more than half the length of the bullet. A dished cavity is made in the base of the bullet to bring it to the proper weight.

=Projectiles, Theory of.= Is the investigation of the path, or _trajectory_ as it is called, of a body which is projected into space. A body thus projected is acted upon by two forces, the _force of projection_, which, if acting alone, would carry the body onwards forever in the same direction and at the same rate; and the _force of gravity_, which tends to draw the body downwards towards the earth. The force of projection acts only at the commencement of the body’s motion; the force of gravity, on the contrary, continues to act effectively during the whole time of the body’s motion, drawing it farther and farther from its original direction, and causing it to describe a curved path, which, if the body moved in a vacuum, would be accurately a parabola.

_Trajectory in Vacuo._--This general theory is not the object of the present discussion, but simply the theory of projectiles as far as it relates to fire-arms. The path that the centre of gravity of a projectile would describe in _vacuo_ would be a parabola, and the greatest range given by an angle of fire of 45°. Under the same angles of fire the range would be proportional to the squares of the velocities, the velocity least at the summit of the trajectory, and the velocities at the two points in which the trajectory cuts the horizontal plane equal. The time of flight would be given for an angle of 45° by the formula:

_T_ = ¹⁄₄√_X_

In which _T_ represents the time of flight, and _X_ the range expressed in feet. These results are found to answer in practice for projectiles which experience slight resistance from the air, or for heavy projectiles moving with low velocities, as is usually the case with those of mortars and howitzers, for which, within certain limits, the above results are sufficiently accurate in practice.

_Trajectory in Air._--A body moving in air experiences a resistance which diminishes the velocity with which it is animated. Thus it has been shown that certain cannon-balls do not range one-eighth as far in the air, as they would if they did not meet with this resistance to their motion, and small-arm projectiles which have but little mass are still more affected by it. This resistance is expressed by the formula:

( _v_) _P_ = _A_{p}R_²(1 + ---)_v_²; ( _r_)

in which _P_ represents the resistance in the terms of the unit of weight, _v_ the velocity, and _pR_² the area of a cross-section of the projectile, _A_ the resistance in pounds on a square foot of the cross-section of a projectile moving with a velocity of one foot, _r_ is a linear quantity depending on the velocity of the projectile. For all service spherical projectiles _A_ is .000514, and for all service velocities _r_ is 1.427 feet; the value of _A_ for the rifle-musket bullet is .000358; hence, the resistance of the air is about one-third less on the ogival than on the spherical form of projectile. _A_ being a function of the density of air, its value depends on the temperature, pressure, and hygrometric condition. It has been demonstrated that the final velocity of a projectile falling in the air is directly proportional to the product of its diameter and density, and inversely proportional to the density of the air; the retarding effect of the air is less on the larger and denser projectiles, and for the same caliber an oblong projectile will be less retarded by the air than one of spherical form and consequently with an equal, perhaps less, initial velocity, its range will be greater. It has also been shown that great advantage in point of range is obtained by using large projectiles instead of small ones, solid projectiles instead of hollow ones, leaden projectiles instead of iron ones, and oblong projectiles instead of round ones. The ogival form, or the form of the present rifle-musket bullet, experiences less resistance in passing through the air than any other known. In consequence of the variable nature of the resistance of the air, it has been found impossible to find an accurate expression for the trajectory. Capt. Didion, of Metz, has, however, found an approximate solution; he states that all cases of the movement of a projectile may be divided into three classes: 1st. When the angle of projection is slight or does not exceed 3°, as in the ordinary fire of guns, howitzers, and small-arms,--for slight variations of the angle of projection above or below the horizontal, the form of the trajectory may be considered constant, and when the object is but slightly raised above or depressed below the horizontal plane, it may be considered as in this plane. 2d. When angles of projection do not exceed 10° or 15°, as in the ricochet fire of guns, howitzers, and mortars. 3d. When the angle of projection exceeds 15°, as is the case in mortar fire. For each of these cases he has deduced formulæ, by means of which the range, time of flight, etc., can be determined. As a projectile rises in the ascending branch of its trajectory, its velocity is diminished by the retarding effect of the air, and the force of gravity, in consequence of the resistance of the air alone, the velocity continues to diminish to a point a little beyond the summit of the trajectory, where it is a minimum, and from this point it increases, as it descends, under the influence of the force of gravity, until it becomes uniform, which event depends on the diameter and weight of the projectile, and the density of the air.

The inclination of the trajectory decreases from the origin to the summit, where it is nothing, it increases in the descending branch from the summit to its termination, and if the ground did not interpose an obstacle, it would become vertical at an infinite distance. An element of the trajectory in the descending branch has a greater inclination than the corresponding element of the ascending branch. Strictly speaking, therefore, the trajectory of a projectile in air is not a parabola, but is an exponential curve with two asymptotes, the first the axis of the piece, which is tangent to the trajectory when the initial velocity is infinite, the second a vertical line toward which the trajectory approaches, as the horizontal component of the velocity diminishes and the effect of the force of gravity increases. The curvature of the trajectory increases in the ascending branch to a point a little beyond the summit. The point of greatest curvature is situated nearer the summit than the point of minimum velocity. In the fire of mortar-shells, under great angles of projection, the trajectory may be considered as an arc, in which the angle of fall is slightly greater than the angle of projection. In the formulæ deduced by Didion, in consequence of considering the inclination of the trajectory as constant, the resistance of the air is slightly underestimated in the more inclined portions of the trajectory or at the beginning and end, and slightly overestimated in the less inclined portions or about the summit. It follows that the calculated trajectory will at first rise above the true one, then pass below it and again pass above it; the calculated ranges are therefore slightly in excess of the true ones.

_Trajectory of Oblong Projectiles._--From the law of inertia, a rifle projectile moves through the air with its axis of rotation parallel to the axis of the bore. Hence it follows that an oblong projectile, fired under a low angle of projection, presents a greater surface toward the earth, and less parallel to it, than a round projectile of the same weight, consequently the vertical component of the resistance of the air is greater, and the horizontal component less, in the first case than in the second. The effect of this will be to give an oblong projectile a flatter trajectory and longer range than a round one.

_Deviation of Projectiles._--The path described by the centre of inertia of a projectile, moving under the influences of gravity and the tangential resistance of the air, is called the _normal trajectory_. In practice, various causes are constantly at work to deflect a projectile from its normal path. All deviating causes may be divided into two classes,--those which act while the projectile is in the bore of the piece, and those which act after the projectile has left it. The first class includes all the causes which affect the initial velocity, and give rotation to the projectile; the second includes the action of the air.