A Military Dictionary and Gazetteer / Comprising ancient and modern military technical terms, historical accounts of all North American Indians, as well as ancient warlike tribes; also notices of battles from the earliest period to the present time, with a concise explanation of terms used in heraldry and the offices thereof. The work also gives valuable geographical information. Compiled from the best authorities of all nations. With an appendix containing the Articles of war, etc.

by Thomas Wilhelm

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.