Chapter XXXIX: Part 39

_Sea-Coast Carriages_ are divided into barbette front-pintle and barbette centre-pintle carriages, casemate, and flank-defense carriages; depending upon the part of the work in which they are mounted. The casemate-carriage differs from the barbette in being much lower. Sea-coast carriages are now chiefly made of wrought iron. All are composed of two principal parts, viz.: the gun-carriage and chassis. The gun-carriage is composed of two cheeks, held together by two plates of boiler-iron, called the front and rear transoms respectively. Each cheek is formed of two pieces of boiler-iron cut to a triangular shape, separated at the edges by interposing the vertical portion or web of a T-shaped bar. The horizontal branches project over each side to form a double rim, which gives stiffness to the cheeks. Flat bars of iron are also placed between the plates at suitable intervals to stiffen the cheeks in the direction in which the weight and recoil of the piece bear upon them. All these parts are held together by screw-bolts. The motion to and from battery is regulated in the 8- and 10-inch carriages by a pair of eccentric truck-wheels, called manœuvring-wheels, which work on an axle-tree placed underneath and a little in front of the centre of the trunnions. When it becomes necessary to check the recoil of the gun-carriage, the wheels are thrown out of gear by means of a handspike inserted in the socket attached to the end of the axle-tree, and the carriage moved on sliding friction. When the gun is to be moved into battery, the wheels are thrown into gear in a similar manner, and the front of the carriage moves on rolling friction. The manœuvring-wheels mentioned above are fixed on the projecting ends of the axle-tree, the axis of the wheel being eccentric with the axis of the axle-tree. These eccentrics are so arranged that when the centres of the wheels are at their lowest points, the surfaces of the wheels bear on the rails of the chassis, and raise the gun-carriage from it; and when the centres are at their highest points, the surfaces of the wheels do not touch the rails, and the gun-carriage is in contact with them. In case there is no socket connected with the end of the axle-tree, the wheel is thrown into or out of gear, that is, made to bear on the rail of the chassis, or relieved from it, by turning the axle-tree with a wrench placed on the hexagonal end. In the 15-inch carriage there are two pairs of manœuvring-wheels, one pair being placed in front as above described, and the other pair near the rear end of the carriage. In all sea-coast carriages except the flank casemate the elevation and depression are given by a lever, the point of which works in a ratchet cut in the breech of the piece. The fulcrum (ratchet-post) is made of cast iron and rests on the rear transom of the gun-carriage. It has several notches for adjusting the position of the elevating bar. The chassis is a movable railway on which the gun-carriage moves to and from battery. It is composed of two wrought-iron rails inclined 3° to the horizon, and united by transoms as in the gun-carriage. In addition to the transoms, there are several diagonal braces to give stiffness to the chassis. For the 10-inch and smaller carriages, the chassis-rails are single beams of rolled iron, 15 inches deep; for all calibers above, the rails are made of long rectangular pieces of boiler-plate and T-iron, in a manner similar to that of the cheeks of the gun-carriage. In order to move the carriage horizontally in the operation of aiming the piece, the chassis is supported on traverse wheels, which roll on circular plates of iron, fastened to a bed of solid masonry, called the traverse circles. The motion of the gun-carriage is checked front and rear, by pieces of iron bolted to the top of the rails, called hurters and counter-hurters; and it is prevented from slipping off sideways by friction rollers and guides, which are bolted to the cheeks and transoms. In a late modification of the 15-inch carriage, the front eccentric axle is replaced by an ordinary one, dispensing with axle-pawls and friction-bands, the handspike pawls are made double instead of single, with a spring to keep them out of the ratchets, the front set of transoms and diagonal braces are removed from the chassis, and pneumatic or hydraulic buffers to check the recoil are put in with thick braces. When the rear manœuvring-wheels are out of gear, the top carriage touches the rails of the chassis and moves on sliding friction, and when they are in gear the front wheels are also made to touch the rails and the top carriage moves on rolling friction. To prevent the rear manœuvring-wheels from working out of gear while the gun is being run from battery, or jumping in gear when the gun is fired, pawls are provided for locking the rear axle. When no pawls are provided for locking the eccentric axle, it is often necessary for one cannoneer to remain embarred in the axle-socket to prevent the axle from flying out of gear. The 15-inch carriage allows an elevation of about 32° and a depression of about 6°, unless when fitted with pneumatic buffers, when no more than 25° elevation can be given. With the hydraulic buffer which passes along the centre of the chassis and is little used in the U. S. service the elevation is still further diminished. The 10-inch rifle and 13-inch smooth-bore are used with the 13-inch carriage, and the 12-inch rifle and 15-inch smooth-bore on the 15-inch carriage; the 20-inch gun has a separate carriage. The flank-casemate carriage is adapted to the mounting of the 24-pounder iron howitzer in the flanks of casemate batteries. Several modifications have been introduced into the carriages for the experimental rifled guns. For the largest calibers the chassis-rails are deeper in rear than in front. The pintle, set in a heavy flanged block of cast iron, is in front of the chassis, to which it is attached by a strap or heavy plate of iron. The top carriage is manœuvred by chain-gearing worked by a capstan near the rear of the chassis. The elevation is given by a wheel with projecting spokes on the side of the top carriage, which is geared to work a toothed arc attached to the breech of the gun, the reading being given by a pointer on a dial-plate above the wheel. Rubber buffers are placed at the rear transom of the chassis to assist the cylinders to take up the recoil. Friction-plates attached by india-rubber ends to the rear transom take the place of cylinders in certain smaller carriages. In some cases the traverse-wheels are made to relieve the pintle of part of the strain by grooving them to run on heavy traverse-rails and inclining them towards the pintle.

_Mortar-Beds._--Mortars are fired from a bed; in the U. S. service there are three kinds of mortar-beds in use in the siege service; the 8-inch, 10-inch, and the Coehorn; the first two differ only in dimensions. They are made of wrought iron and put together after the manner of the sea-coast gun-carriage. The different parts are the cheeks, which, like those of the gun-carriage, are triangular in shape, and two transoms connecting the cheeks together. At the end of each cheek are projections, called front and rear notches, underneath which the cannoneers embar with their handspikes to move the bed on the platform; there are also two front and two rear manœuvring-bolts for the same purpose. The elevation and depression are given as in the gun-carriage by embarring with the iron elevating bar through the fulcrum into the ratchets on the breech of the mortar. The Coehorn-bed is made of a block of oak wood, in one piece, or two pieces joined together with bolts. A recess for the trunnions and part of the breech is made in the top of the bed, and the trunnions are kept in their places by plates of iron bolted down over them. Two iron handles are bolted to the bed on each side, by which four men can carry the bed with the mortar in its place, the entire weight being only 296 pounds. Sea-coast mortar-beds are similar to those for siege purposes, but they have eccentric truck-wheels for manœuvring the mortar-bed on the platform and the manœuvring-bolts are omitted. The 13-inch sea-coast mortar is now mounted upon a centre pintle-carriage. The usual bed, now become the top carriage, is placed upon a chassis resting on a platform. The top carriage has a crane attached to the left cheek, and to the inside of the right cheek is attached a pawl worked from the front, for locking the eccentric axle in and out of gear, and the carriage is strengthened by an additional rear transom about 5 inches wide, the pipe being omitted. The chassis has the usual appliance for throwing this class of carriages into gear, and in addition an eccentric axle placed at right angles to and supported by a double front transom, and carrying a traverse wheel, by means of which motion is communicated to the chassis. The chassis is otherwise transomed and braced in accordance with the system. Heretofore nearly all sea-coast carriages were made of wood, but in consequence of the great difficulty of preserving this material from decay, especially when exposed to the dampness of casemates, they have nearly all been replaced by wrought iron. The carriages principally employed for the transportation of ammunition, implements, and materials for repairs, are caissons, mortar-wagons, forges, and battery-wagons.

_The Caisson._--Caissons are used for conveying ammunition for a field-battery; all are similar in form. It is a four-wheeled carriage, consisting of two parts, one of which is a limber similar to that of the gun-carriage, and connected in a similar way by a wooden stock and lunette. On the axle-body of the rear part and parallel to the stock are placed three rails, upon which are fastened two ammunition-chests, one behind the other, and similar to the one on the limber; so that the caisson has three ammunition-chests, which will seat 9 cannoneers. The interior compartments of the ammunition-chests vary according to the nature of the ammunition with which they are loaded. In rear of the last chest is placed a spare-wheel axle of iron, with a chain and toggle at the end of it. On the rear end of the middle rail is placed a carriage hook similar to a pintle-hook, to which the lunette of a gun-carriage whose limber has become disabled may be attached, and the gun carried off the field. The caisson has the same turning capacity and mobility as the gun-carriage, so that it can follow the piece in all its manœuvres, if necessary. It also carries a spare-wheel, spare-pole, etc. The principal parts of the caisson are: stock, or middle-rail; it has an iron lunette on its front end; side-rails, front foot-board, rear foot-board, middle-chest, rear-chest, spare-wheel axle; it has a body, two ribs, and a chain and toggle to secure the wheel; there are also two stays for the axle; lock-chains, fastened to lock-chain bridles under the front ends of the side-rails, and held up by lock-chain hooks fastened to the outside of the side-rails; spare-pole, spare-pole key, key-plate, chain, and pin; the key-plate is fastened to the under side of the lunette; the key is attached to the left side of the stock by a chain and eye-pin; carriage-hook, for attaching a carriage that has lost its limber; wheel-guard plates, spare-pole ring, held by the axle-strap; ring-bolt for spare hand-spike, key-plate and key, on the right side of the middle-rail; key-plate, chain, and key for the shovel-handle, on the inside of the right side-rail; middle assembling-bar, of iron; it has two ears in the middle to serve as stay-plates for the middle-chests, and a slot for the axe on the right of the middle-rail; rear assembling-bar; it supports the spare-wheel axle, and has a slot for the pickaxe on the left of the middle-rail. Axle, the axle-body, being notched to receive the middle-rail and tenoned to fit into the notches in the side-rails; staples for tool-handles; they are driven into the top of the axle-body in front of the iron axle-tree, one for the shovel-handle near the right side-rail, the other for the handle of the pickaxe on the left of the middle-rail. Wheels of all artillery carriages are similarly constructed; they differ, however, in the size and strength of certain parts, depending on the size of the carriage to which they are attached. The principal parts are: the nave, the nave-bands, the nave-box, the spokes, the felloes, and the tire. The nave constitutes the central portion of the wheel, and distributes the pressure of the axle-arm to the spokes. It is generally made of a single piece of wood, and strengthened by four iron bands called the nave-bands. It is also pierced with a conical hole for the axle-arm; and to diminish wear and friction, it is lined with a box of brass or cast iron, called the nave-box. The spokes serve to transmit the pressure of the load to the rim of the wheel. In all artillery carriages there are seven felloes and fourteen spokes. The felloes are the wooden segments which form the rim, and are joined together at their ends by wooden pins, or dowels. The tire is a strong band of iron, shrunk tightly around the felloes, to hold them together, and protect the rim from wearing away by contact with the ground.

_Mortar-wagons_ are designed for the transportation of siege-mortars and their beds, or of guns or large shot, and shells. A limber similar to the one for siege-gun carriages is used with it. The body consists of a platform of rails and transoms resting on an axle-tree. The stock is formed by prolonging the two middle-rails. The side-rails projecting to the rear form supports for the pivots of a windlass-roller. This roller is used to load guns and mortars on the wagon by drawing them up the stock. A muzzle-bolster on the stock near the limber, and a breech-hurter near the hind part of the wagon, are provided and used when long pieces are transported on it. Mortars are usually carried mounted on their beds.

The _traveling-forge_ is a complete blacksmith’s establishment, which accompanies a battery for the purpose of making repairs and shoeing horses. It consists of a body, upon which is constructed the bellows-house, etc., and the limber, which supports the stock in transportation. The body is composed of two rails, a stock, and an axle-tree. The bellows-house is divided into the bellows-room and iron-room. Attached to the back of the house is the coal-box, and in front of it is the fireplace. From the upper and front part of the bellows an air-pipe proceeds in a downward direction to the air-box, which is placed behind the fireplace. The vise is permanently attached to the stock, and the anvil, when in use, is supported on a stone or log of wood, and when transported is carried on the hearth of the fireplace. The remaining tools are carried in the limber-chest. When in working order the point of the stock is supported by a prop. Nomenclature of the traveling-forge body: Lunette, prop, vise, stock, wheel-guard plates, stock-stirrup, fireplace, back of fireplace, air-back, wind-pipe, bellows, ribs, hinges, hook, fulcrum, hook and staple, roof of bellows-house, bows, studs, girders, end-boards, bottom-boards, side-rail, lock-chain hook, coal-box, lid or roof, handles, hinges, turnbuckle, and hasp. A new pattern of field-forge has been proposed by Col. Laidley, U. S. Ordnance Corps.

The _battery-wagon_ is employed to transport the tools and materials for repairs. Among the tools are those for carriage-makers, saddlers, armorers, and laboratorians’ use, scythes and sickles for cutting forage, and spare implements for the service of the piece. The body of the battery-wagon is a large, rectangular box, covered with a roof of painted canvas; and to the back part is attached a rack for carrying forage. The bottom of the body is formed of one middle- and two side-rails, resting on a stock and axle-tree, as in the traveling-forge. The tools and materials of the battery-wagon are carefully packed in the manner prescribed by the Ordnance Manual, in order that no difficulty may be experienced in finding a particular article when wanted. The smaller articles are carried in boxes properly lettered and numbered. The traveling-forge and battery-wagon are not confined to the service of field-batteries, but are used with siege and sea-coast carriages as occasion may require. Nomenclature of the battery-wagon body: Lunette, stock, wheel-guard plate, lock-chain, lock-chain bridle, lock-chain hook, studs, side-rails, upper rails, hinges, bows, cover-boards, cover-strap and turnbuckle, hasp, side-boards, stays, bottom-rails, bottom-boards, cross-bars, forage-rack, including chains, sides, and bars.

=Ordnance, Construction of.= The present condition of gun construction is mainly experimental. Iron in one form or another is the only material used for heavy artillery, but the particular form in which it is to be used, whether as cast, wrought, or steel, or whether in bars, coils, or ingots, or in combination,--as, for instance, steel or wrought iron interior and cast iron or wire-wrapped or hooped exterior,--is still undecided, and it is left for experiments which are still in progress, or to be made hereafter, to decide which is best. In the United States, cast iron is used for smooth-bore guns, and also for rifle guns, but as its use for the latter has not proved satisfactory, experiments are now being made with wrought iron lined and with wire-wrapped and other built-up guns, with fair prospect of success. In England, modern gun construction at one period inclined to the use of a steel or wrought iron interior tube, strengthened by an exterior casting of iron, which is the system of Palliser and Parsons. But the preference for the inventions of Sir William Armstrong, improved by those of Fraser, have resulted in the exclusive use, in that country at present, of the system of these two inventors. This method of gun construction is, in brief, a steel core (or body of the gun) strengthened by three or more exterior tubes of coiled wrought iron. This system is at present popularly known as the “Woolwich,” but sometimes called the “Elswick,” from the place where Sir William Armstrong’s works are now located. In Germany and Russia, and some other European nations, the Krupp system of heavy forgings of steel ingots is preferred. This last is by far the most expensive, and does not always produce the most durable guns. The question of breech- or muzzle-loading is still an undecided one. (See BREECH-LOADING and BREECH-MECHANISM.) The Germans prefer the first named, as do the French, Austrians, and Russians, for large calibers and for most small guns, while the English, after several years’ trial of the first, have of late abandoned its use and returned to the muzzle-loader, though the question has again been recently agitated. In the United States, experiments still going on have not yet demonstrated which principle is the best suited to the gun construction used in America. The advantages of loading at the breech with heavy guns are numerous and great; but the serious mechanical difficulties (see BREECH-MECHANISM) of perfecting the movable breech attachment have militated against its adoption, especially in a country committed like the United States to the use of cast iron. During the half-decade (1855-60), and the succeeding decade (1860-70), enormous strides were made in gun construction and in that of carriages and projectiles, and the manufacture of gunpowder.

_Cast Metal Guns._--The principles which govern the construction of homogeneous cast metal guns as established by long practice will be considered under the following heads:

_Exterior Form._--The exterior of cannon is generally divided into five principal parts, viz.: the breech, the first reinforce, the second reinforce, the chase, and the swell of the muzzle.

The _breech_ (see BREECH) is the thickness of metal in the prolongation of the axis of the bore, and should be at least equal to one and a quarter times the diameter of the bore; a less thickness has been found insufficient for heavy iron guns.

The _first reinforce_ (see REINFORCE) extends from the base-ring to the seat of the ball, and is the thickest part of the piece, for the reason that the pressure of the powder is found to be greatest before the projectile is moved far from its place. In shape this reinforce was formerly made slightly conical, under the impression that the pressure was greater at the vent than at the seat of the projectile; but it is now made cylindrical throughout. The thickness of bronze cannon at the seat of the charge is less than for iron guns.

The _second reinforce_ (see REINFORCE) connects the first reinforce with the chase. It is made considerably thicker than is necessary to resist the action of the powder, in order to serve as a proper point of support for the trunnions, and to compensate for certain defects of metal liable to occur in the vicinity of the trunnions of all cast cannon, arising from the crystalline arrangement and unequal cooling of the different parts.

_The Chase_ (see CHASE).--From the extremity of the second reinforce cannon taper more or less rapidly to the vicinity of the muzzle; this part called the chase constitutes the largest portion of the piece in front of the trunnions. The thickness of metal in the chase should be sufficient to resist the striking of the ball against the side of the bore. This injury being greater in bronze and soft iron guns, their taper is less than in cast-iron cannon. In the construction of bronze guns, the thickness of metal at the neck or thinnest part is about five-elevenths of that at the first reinforce. All projections on the surface of cannon not absolutely necessary for the service of the piece are omitted in cannon of _late models_. This omission simplifies their construction, renders them easier to clean, and obviates certain injurious strains that would otherwise arise from unequal cooling in fabrication.

_Swell of the Muzzle._--The enlargement called swell of the muzzle was generally regarded as necessary, inasmuch as the metal situated immediately at the muzzle is supported only in rear, and it was thought necessary to increase its thickness in order to enable it to resist the action of the projectile at this point. At present, however, the tendency is to reduce the size of the swell of the muzzle and to omit it entirely on all sea-coast cannon.

_Interior Form of Cannon._--The interior of a cannon may be divided into three distinct parts, viz.: the vent, or channel which communicates with the charge; the seat of the charge or chamber, if its diameter be different from the rest of the bore, and the cylinder, or that portion of the bore passed over by the projectile (see appropriate headings).

The _vent_ (see VENT) is perpendicular to the axis of the piece, and the interior orifice is at a distance from the bottom of the chamber equal to a quarter of its diameter, or at the junction of the sides of the chamber with the curve of the bottom. Experiment has shown this position to be the most favorable to the full development of the force of the charge, and to be least injurious to the piece. The size of the vent should be as small as possible, in order to diminish the escape of the gas and the erosion of the metal which results from it. In the U. S. service all vents are 0.2 inch in diameter. Experiment has, however, shown that the actual loss of force by the escape of the gas through the vent, as compared to that of the entire charge, is inconsiderable, and in practice may be neglected. In the U. S. service some pieces are made with two unbushed vents which are situated in two vertical planes on opposite sides of and parallel to the axis of the bore, and at a distance from it of one-half the radius of the bore. The left vent is bored entirely through, the other stops one inch short of the surface of the bore. When the open vent is too much enlarged by wear for further use, it is closed with melted zinc, and the other is bored out. Each vent is calculated to endure at least five hundred service rounds. In English guns of old model, the vent is placed four-tenths of the length of the cartridge from the bottom of the bore. In most breech-loaders, as well as many large modern muzzle-loaders, the vent is in the axis of the piece through the breech.

_Seat of the Charge._--The form of the seat of the charge, or that part of the bore of a fire-arm which contains the powder, will have an effect on the force of the charge and the strength of the piece to resist it. The considerations most likely to affect the force of the powder are the form of the surface and its extent compared with the inclosed volume. To obtain the full force of the charge it is necessary that the inflammation be nearly completed before the gas begins to escape through the windage, and the projectile is sensibly moved from its place, and as the tension depends much upon the heat evolved by the combustion, the absorbing surface should be a minimum compared with the volume. In cannon where the charge of powder is large, the form of the seat of the charge is simply that of the bore prolonged; this arrangement, when compared with the chamber, makes the absorbing surface of the metal a minimum and reduces the length of the charge, so that its inflammation will be as complete as possible before the gas escapes and the projectile is moved. To give additional strength to the breech, and to prevent the angle formed by the plane of the bottom and sides of the bore from becoming a receptacle for dirt and burning fragments of the cartridge-bag, it is rounded with the arc of a circle, whose radius is one-fourth the diameter of the bore at this point. Instead of being a plane bottom it is sometimes made hemispherical, tangent to the surface of the bore. In all United States cannon of the most recent model, the bottom of the bore is a semi-ellipsoid; this is thought to fulfill the condition of strength more fully than the hemisphere. With light pieces, in which it is necessary to use small charges of powder, if the charge were made into a cartridge of a form to fit the bore its length would be less than its diameter, and being ignited at the top, a considerable portion of the gas generated in the first instance of inflammation would pass through the windage, and a part of the force of the charge would be lost. To obviate this defect, to give the cartridge a more manageable form in loading, and to make the surface a minimum as regards the volume, the diameter of this part of the bore is reduced so as to form a chamber. The shape of the chambers of fire-arms is either cylindrical, conical, or spherical; the effect of these different forms of chambers on the velocity of the projectile will be modified by the size of the charge and the length of the bore. Up to a charge of powder equal to one-seventh of the weight of the projectile, and a length of bore equal to 9 or 10 calibers, experience shows that the presence of a chamber is advantageous, but beyond these it possesses no advantages to compensate for its inconvenience. For very small charges of powder and short lengths of bore, the cylindrical chamber gives better results than the conical chamber. For the same capacity, the conical chamber gives a shorter cartridge, and is therefore better suited to the rapid inflammation of a large charge of powder than the cylindrical chamber.

The Gomer chamber belongs to this class. (See GOMER CHAMBER.) The spherical chamber was formerly used particularly in mortars, but owing to the inconveniences which attend its construction and use, and its liability to deterioration, it is now entirely abandoned. In all the regulation guns of the U. S. land service, the bottom of the bore is a semi-ellipsoid. The adoption of this form simplifies the whole subject of chambers, and it is found to give increased ranges for small charges. No very careful experiments have been made to determine in a general way the effect of chambers on the strength of cannon; but late experience indicates that cylindrical chambers in heavy iron guns have an injurious effect on their endurance, and they have consequently been abandoned in these pieces.

_The Bore_ (see BORE).--The length of the bore has an important effect on the velocity of the projectile, and it was formerly supposed that the longest pieces gave the greatest ranges; this belief was in a great measure due to the slow rate of burning of mealed powder, which was originally used in cannon, but was entertained even after gunpowder received its granular form. When a gun is discharged, the accelerating force is due to the expansive effort of the inflamed powder, which reaches its maximum when the grains of the charge are completely converted into vapor and gas. This event depends on the size of the charge, and the size and velocity of combustion of the grains. With the same accelerating force, the point at which a projectile reaches its maximum velocity depends on its density, or the time necessary to overcome its inertia. The retarding forces are:

(1) The friction of the projectile against the sides of the bore; this is the same for all velocities, but different for different metals.

(2) The shocks of the projectile striking against the sides of the bore; these will vary with the angle of incidence, which depends on the windage and the extent of the injury due to the lodgment and balloting of the projectile.

(3) The resistance offered by the column of air in front of the projectile; this force will increase in a certain ratio to the velocity of the projectile and length of the bore. As the accelerating force of the charge increases up to a certain point, after which it rapidly diminishes as the space in rear of the projectile increases; and as the retarding forces are constantly opposed to its motion, it follows that there is a point where these forces are equal, and the projectile moves with its greatest velocity; it also follows that after the projectile passes this point its velocity decreases, until it is finally brought to a state of rest, which would be the case in a gun of great length. Elaborate experiments have been made in this country and abroad to determine accurately the influence which the length of the piece exercises on the velocity of its projectile. The experiments made by Maj. Mordecai of the U. S. Ordnance Department with a 12-pounder gun, show that the velocity increases with the length of the bore up to 25 calibers; but that the entire gain beyond 16 calibers, or an addition of more than one-half to the length of the gun, gives an increase of only one-eighteenth to the effect of a charge of four pounds. It follows from the foregoing that the length of bore which corresponds to a maximum velocity depends upon the projectile, charge of powder, and material of which the piece is made, and taking the caliber as a unit of measure, it is found that this length is greater for small-arms which fire leaden projectiles than for guns which fire solid iron shot, and greater for guns than for howitzers and mortars, which fire hollow projectiles. For the same charge of powder it may be said that the initial velocity of a projectile varies nearly with the fourth root of the length of the bore, provided the variation in length be small.

_Manufacture of Cannon._--Cannon for the U. S. service are made by private founders. The material and product of the casting are under the supervision of an ordnance officer, who receives the pieces only after they have satisfied all the conditions imposed by the regulations of the service. There are several foundries for making cast-iron cannon. Wrought-iron field cannon are principally made at the Phœnixville Iron-Works, Pa. There are also several private establishments where special cannon are made. The several operations of manufacturing cannon are, molding, casting, cooling, and finishing.

_Molding_, in general terms, is the process by which the cavity of the form of the gun is obtained by imbedding a wooden model in sand, and then withdrawing it. The wooden model is technically called the pattern, and the sand is confined in a box, which is divided into two or more parts for convenience in withdrawing the pattern. The pattern of the piece to be cast, somewhat enlarged in its different dimensions, is composed of several pieces of hard wood, well seasoned, or, for greater durability, of cast iron. The first piece of the model comprises the body of the piece from the base-ring to the chase-ring; the swell of the muzzle, and the sprue, or dead-head, are formed of the second piece; the breech, of the third; and the trunnions, of the fourth and fifth pieces. The sprue, usually called the “head,” is an additional length given to the piece, for the purpose of receiving the scoria of the melted metal as it rises to the surface, and furnishing the extra metal needed to feed the shrinkage. Its weight also increases the density of the lower portion of the piece. The breech is slightly lengthened in the direction of the knob of the cascabel, to form a square projection by which the piece can be held when being turned and bored. The best material for the mold is dry, hard, angular, and refractory sand, which must be moistened with water in which strong clay has been stirred, to make it sufficiently adhesive; when not sufficiently refractory, the sand is vitrified by the high temperature of the melted metal, and protuberances--not easily removed--are formed on the casting. When not sufficiently coarse and angular, the materials cannot be so united as to preserve the form of the molds. The mold is formed in a case of cast iron, and termed the “box,” or the “flask,” consisting of several pieces, each of which has flanges perforated with holes for screw-bolts and nuts, to unite the parts firmly. To form the mold, the pattern for the sprue and muzzle, previously coated with pulverized charcoal or coke, moistened with clay-water to prevent adhesion, is placed vertically on the ground, muzzle part up, and carefully surrounded by the corresponding parts of the jacket. When properly adjusted, the sand, prepared as above, is rammed around it. The model for the body of the piece is then placed on the top of this, and the corresponding parts of the jacket correctly secured, and filled in succession with the molding composition. The patterns for the trunnions and rimbases are bolted to the model of the piece, and when the sand is rammed firmly around these, the bolts are withdrawn, this part of the mold completed, and the end-plates screwed on. After completing the mold for the body of the piece, the model for the cascabel is properly adjusted and the mold completed. Care is taken to cover each portion of the model with the coke-wash mentioned above, and to sprinkle dry sand upon the top of the mold in each piece of the jacket, to prevent adhesion, so that the portions of the mold may be separated. In the body of the sand, a channel for the introduction of the metal is formed in the same manner as the mold cavity. It enters at the bottom of the mold, to prevent the bottom from being injured by the falling metal, and in an oblique direction, to give a circular motion to the metal as it rises in the mold, and thereby prevent the scoria from adhering to the sides. When the mold is completed, the parts of the flask are carefully taken apart, and the pieces of the model withdrawn from the mold contained in them. If any portions of the mold be injured in withdrawing the model, they are repaired, and the interior of the mold is covered with coke-wash; after which the several parts are placed in an oven to be gradually and perfectly dried. When this is accomplished, the parts are carried to a pit, where they are united and secured in a vertical position, with the breech below. Any portion of the sand broken off during the movements and adjustments should be replaced, and the whole of the interior covered with coke-wash. The object of coke-wash is to prevent the sand from adhering to the melted metal, which, when prepared, is made to flow in at the entrance of the side-channel. As the metal rises in the mold, a workman agitates it with a long pine stick, to cause the scoria and other impurities to rise to the surface, and brings them toward the centre of the mold, to prevent their entering the cavities for the trunnions.

_Cooling._--After the mold is placed properly in the pit, it is usual to surround the box with sand, at least as high as the trunnions of the gun. This is done to prevent rapid cooling. With guns as heavy as 24-pounders, this sand is not removed for three days, and as the gun is heavier the time is prolonged, and is from seven to eight days for the 10-inch columbiad. At the proper time the sand is removed, and the gun, still imbedded in the box and sand of the mold proper, is hoisted out, the box taken off, and when nearly cold, the gun cleaned of the sand.

_Boring and Turning._--A cannon is bored by giving it a rotary motion around its axis, and causing a rod armed with a cutter to press against the metal in the proper direction. The piece, supported in a rack, is carefully adjusted, with its axis horizontal, and made to revolve on this axis by machinery attached to the square knob on the cascabel. After adjustment, the sprue-head is first to be cut off. This is effected by placing a cutter opposite the point at which the section is to be made, and pressing it against the metal whilst the piece is turning. The head being cut off, and the cutter removed, the boring is commenced by placing the boring-rod, armed with the first cutter, called the piercer, in the prolongation of the axis of the piece, and pressing it against the metal. The piercer is used till it penetrates to the bottom of the chamber, after which a second cutter, or reamer, is attached to the boring-rod, and with this the boring is made complete to the round part of the chamber. The reamer is then removed and its place supplied by the chamber-cutter, which gives the necessary form and finish to that part of the bore. In hollow-cast cannon the piercer is dispensed with. Whilst the boring is taking place the workman contrives to finish the turning of all the exterior of the piece except the portion between the trunnions, which is afterwards planed off in another machine. These operations having been completed, the piece is placed in the trunnion-machine, and the trunnions are turned down to the proper size. Care is taken to make the trunnions of the same diameter, and perfectly cylindrical. Their axes should be in the same right line, perpendicular to the axis of the piece and intersecting it.

_Boring the Vent._--Whilst in the trunnion-lathe, the axis of the piece is inclined to the horizon at the angle the vent is to make with it. A drill is placed vertically over the point where the vent is to be bored, and pressed against the metal whilst a rotary motion is given to it by hand or machinery. The time required to finish a cannon, ready for inspection, depends upon its size, or from three to four weeks for a 24-pounder gun, and six weeks for an 11-inch gun.

_Cast Metal Guns, Modern Improvements in._--The first great step in this direction was taken by Gen. Rodman of the U. S. Ordnance Corps. It was his investigation into the crystallization of cast iron which led to the abolition of sharp angles or projections in the form of cannon. His reputation, however, rests mainly upon the principle of _hollow casting_. The general form of the old casting is that of a _solid_ frustrum of a cone; it is therefore cooled from the exterior, which causes the thin outer layer to contract first, and forces the hotter and more yielding metal within towards the opening of the mold. Following this the adjacent layer cools and tends to contract, but the exterior layer to which it coheres has become partially rigid and does not fully yield to the contraction of the inner layer. The result is, the cohesion of the particles of the inner layer is diminished by a force of extension, and that of the outer layer increased by a force of compression. As the cooling continues this operation is repeated, until the whole mass is brought to a uniform temperature, and the straining force is increased to an extent which depends on the size and form of the mass, the rapidity with which it is cooled, and the contractibility of the particular metal used. The foregoing considerations led Rodman to cast the gun hollow and to cool it from the interior, to reverse the strains by external cooling, and make them contribute to the endurance rather than to the injury of the piece. The method employed is to carry off the internal heat by passing a stream of water through a hollow core, inserted in the centre of the mold cavity before casting, and to surround the flask with a mass of burning coals, to prevent too rapid radiation from the exterior. Results show that cast-iron cannon made by this plan are not only stronger, but are less liable to enlargement of the bore from continued firing. All large American guns of cast iron, including the cases for the experimental rifles, are now cast on the Rodman plan. The plan has also been adopted by most of the nations of Europe that use cast-iron guns,--France, Sweden, Italy, etc.

For improvements in _bronze_, see the methods of Dean and Uchatius, ORDNANCE, METALS FOR.

The following are among the best known of cast metal homogeneous guns:

_Columbiad._--The columbiads are a species of sea-coast cannon containing certain qualities of the gun, howitzer, and mortar; they are long, chambered pieces capable of projecting solid shot and shells with heavy charges of powder, at high angles of elevation. The columbiad was invented by Col. Bomford, late of the U. S. service; the model was afterwards changed by lengthening the bore and increasing the weight of metal. (See ORDNANCE, HISTORY OF.) It was afterwards discovered that these pieces did not possess the requisite strength, and they were degraded to the rank of shell guns, and their places supplied by pieces of improved model. The change consisted in giving greater thickness of metal in the prolongation of the axis of the bore, which was done by diminishing the length of the bore itself; in substituting a hemispherical bottom to the bore, and removing the cylindrical chamber; in removing the swell of the muzzle and base-ring, and in rounding off the corner of the breech. In 1860 the model prepared by Capt. Rodman was adopted for all sea-coast cannon, and is essentially the same as the one described below.

_Paixhan Gun._--See ORDNANCE, HISTORY OF.

_Dahlgren Gun._--The guns constructed after the plan of Admiral Dahlgren of the U. S. navy, are used principally in the U. S. sea service. Those of large caliber are made of cast iron, solid, and cooled from the exterior. To produce uniformity in the cooling, the piece is cast nearly cylindrical, and then turned down to the required shape. The thickness of the metal around the seat of the charge is a little more than the diameter of the bore, as is true of nearly all the cast-iron guns. The chase, however, tapers more readily than in other cast-iron guns; they are smooth-bored, and the chamber is of the Gomer form. The principal guns of this system are of 9- and 11-inch caliber. A piece of 10-inch caliber has, however, been introduced into the navy for firing solid shot. The 15- and 20-inch naval guns are shaped exteriorly after the Dahlgren pattern, but are cast hollow, and have the elliptical chamber of the Rodman system.

_Napoleon Gun._--A bronze field-piece in the U. S. service. See NAPOLEON GUN.

_Rodman Gun._--The principal difficulty formerly experienced in manufacturing very large cast-iron cannon was the injurious strain produced by cooling the casting from the exterior. Gen. Rodman of the U. S. Ordnance Department developed a theory of the strains produced by cooling a casting like that of a cannon (see ORDNANCE, STRAINS UPON), and as a remedy for them proposed that cannon should be cast with a hollow core and cooled by a stream of water or air passing through it. This new mode of casting was afterwards adopted by the War Department. By this system of casting, guns of greatly-increased size and endurance are fabricated. The largest guns employed in the U. S. service (20-inch) are made on the Rodman plan, as well as the 15-inch, 13-, 10-, 8-inch, etc. The external form of Rodman guns is striking, as they are much larger at the seat of the charge than elsewhere. Their outline is made up of curved lines. This form has been almost universally adopted for U. S. guns. The Dahlgren, which preceded it, has nearly the same shape.

The great power demanded at the present day in heavy ordnance, however, cannot be attained by the use of cast iron alone. The difficulties of constructing homogeneous guns of the stronger metals--wrought iron and steel--have given birth in modern times to

_Built-up Guns._--The term “built-up” is applied to those cannon in which the principal parts are formed separately, and then united together in a peculiar manner. One object of this mode of manufacture is to correct the defects of one material by introducing another of opposite qualities, as for instance, trials have been made to increase the hardness, and therefore endurance, of bronze cannon by casting them around a core of steel which formed the surface of the bore. Built-up cannon are not necessarily composed of more than one kind of metal. Some of the most noted are made of steel or wrought iron alone. In this case the defects which we have seen accompany the working of large masses of wrought iron (crystalline structure, cracks, false welds) are obviated by first forming them in small masses, as rings, tubes, etc., of good quality, and then uniting them separately. The mode of uniting a built gun may be by welding the parts, by shrinking, or forcing one over the other, or by screwing them together.

In the _construction of built-up guns_, makers have aimed at the ideal gun which has its strength proportioned to the strain it is called upon to bear in all its parts. All parts of the sides of a cannon are not strained equally, and are therefore not brought to the breaking-point at the same time. Any arrangement of the parts by which the explosive strain is distributed equally over the entire thickness of the piece, necessarily brings a greater amount of resistance into play to prevent rupture. There are two general plans for accomplishing this, viz.: First, by producing a strain of compression on the metal nearest the surface of the bore. This is termed an “initial strain,” and is brought about by shrinking heated bands or tubes around the part to be compressed, or by slipping a tube into the bore, which has been slightly enlarged by heat. In either case it is apparent that the extent of the strain depends on the relative size of the fitting surfaces, and the amount of heat used to produce expansion. Sometimes the parts are forced together by hydraulic pressure after they have been carefully bored and turned to the proper size. The second plan is based on “varying elasticity,” and is accomplished by placing that metal which stretches most within its elastic limit around the surface of the bore, so that by its enlargement the explosive strain is transmitted to the outer parts. By the selection of suitable materials and their proper management, both of these plans may be combined in the same gun, and thereby give it increased strength. See ORDNANCE, CONSTRUCTION OF.

The best-known cannon of the _built-up_ class are:

_Ames Gun._--The rifled guns made by Mr. Horatio Ames, of Falls Village, Conn., are made of wrought iron on the built-up principle. The wrought iron is in the form of rings, made by bending a bar around a mandrel and welding the ends. After turning them in a lathe, two or more of these rings are fitted one within another to form a disk. These disks are welded in succession to a concave breech-piece. Some of these guns have shown remarkable endurance. They are weakest against longitudinal strains.

_Armstrong Gun._--Is so much like the _Woolwich_, which it preceded, that a separate description is unnecessary. See WOOLWICH GUN.

_Blakely Gun._--The most approved pattern of the gun invented by Capt. Blakely combines in its construction the principles of “initial tension” and “varying elasticity,” the object of which is to bring the strength of all the metal of the piece into simultaneous play to resist explosion. It is made of several tubes or barrels, the inner one of which is of low steel, having considerable but not quite enough elasticity. The next tube is made of high steel with less elasticity, and is shrunk on the barrel with just sufficient tension to compensate for the insufficient difference of elasticity between the two tubes. The outer cast jacket, to which the trunnions are attached, is the least elastic of all, and is put on with only the shrinkage by warming it over a fire. The steel tubes are cast hollow and hammered over steel mandrels under steam-hammers; by this process they are elongated, and at the same time the tenacity of the metal is increased, all the steel parts are annealed. Other combinations of iron and steel are used, except wrought iron, which is regarded as objectionable on account of its tendency to stretch permanently. Blakely guns were rifled with one-sided grooves, and are fired with expanding projectiles. This gun is no longer made under that name. As now made it is called the

_Vavasseur Gun_, and is manufactured by Messrs. J. Vavasseur & Co. of the London Ordnance-Works. It is made entirely of the best Sheffield cast steel, except the trunnions, which are wrought iron, and consists of an interior tube and outer tube and a number of hoops. The inner tube is forged from a solid ingot. It is rough bored and turned and then oil tempered. The outer tube and rings are cast hollow and hammered over steel mandrels. They are heated and shrunk on. Theoretically, it is difficult to pick a flaw in the construction of this gun. The rifling used is anomalous. It consists of three _ribs_ instead of grooves projecting into the bore. The projectile has corresponding grooves. These guns have found quite a market in the South American republics.

_Brooke Gun._--This gun was made after the plan of Capt. Brooke for the Confederate service; it resembles Parrott’s in shape and construction, except that the reinforcing band is made up of iron rings not welded together. The rifling is similar to that used in the Blakely guns.

_Fraser Gun._--See WOOLWICH GUN.

_Gatling Gun._--See GATLING GUN.

_Krupp Gun._--See KRUPP GUN.

_Lancaster Gun._--This gun is now little used; it was made of wrought iron. The bore was cut in a spiral form with an elliptical cross-section, and the projectile shaped to fit it, by which means a rotary motion was imparted.