Bronze for cannon (commonly called brass) consists of 90 parts of copper and 10 of tin, allowing a variation of one part of tin more or less; by increasing the proportion of tin, bronze becomes harder, but more brittle and fusible; by diminishing it it becomes too soft for cannon, and at the same time loses a part of its elasticity. Bronze is more fusible than copper, much less so than tin. It is harder, less susceptible of oxidation, and much less ductile than either of its constituents. Its fracture is of a yellowish color, with little lustre, a coarse grain, irregular, and often exhibiting spots of tin which are of a whitish color. The density and tenacity of bronze when cast into the form of cannon, are found to depend upon the pressure and mode of cooling. In consequence of the difference of fusibility of tin and copper, the perfection of the alloy depends much on the nature of the furnace and the treatment of the melted metal. By these means alone the tenacity of bronze has been carried up to 60,000 pounds. Bronze is but slightly corroded by the action of the gases evolved from gunpowder, or by atmospheric causes; but its tin is liable to be melted away at the sharp corners by the great heat generated in rapid firing. It is soft, and therefore liable to serious injury by the bounding of the projectile in the bore. This injury is augmented as the force of the rebound is increased by the elasticity of the metal. It was established by experiments of Maj. Wade of the U. S. Ordnance Corps more than twenty years ago that the tensile strength of bronze is related to its density. It has been discovered since that this density can be produced by artificial compression. Two men claim the honors of the invention—Gen. Uchatius of the Austrian army, and S. B. Dean, an American inventor. The methods are essentially the same. After the gun is cast, steel mandrels slightly conical in shape are driven through the bore by hydraulic pressure,—each being succeeded by one slightly larger,—thus enlarging the bore and compressing the metal surrounding it. It is claimed that the bronze is thus rendered harder and stronger, and the defects above cited in a large measure obviated. The term “steel bronze” or “bronze steel” has been applied to the metal so treated. Many guns have been made of it for the Austrian service,—the largest of which is a 6-inch breech-loader throwing a projectile of 85 pounds. This gun has proved itself slightly superior in power to the same sized Krupp gun of steel.
Aluminium Bronze.—An alloy of 90 parts of copper and 10 of aluminium. It is harder than ordinary bronze; much stronger, being 100,000 pounds to the square inch; it does not tarnish readily. Its properties would seem to especially fit it for a gun metal. Phosphor bronze is an alloy with very similar properties.
Combined Metals.—Numerous trials have been made to improve the strength of cannon by combining two or more metals in such a way that the good qualities of one will counteract the defects of the others. But the only metals used to any extent are those described above. Steel is constantly gaining in favor as a cannon metal. It is now almost exclusively employed throughout Europe, and wherever the Krupp gun is used. The great perfection arrived at by Krupp and others in the manufacture of steel seems to place that metal above all others for gun construction, whilst the difficulty of handling large masses has been overcome by the enormous power of the machinery used. Steel is also sparingly employed both in the United States and England for converting smooth-bore guns into rifles according to the Palliser method, but experiments in the United States have shown that it is inferior to wrought iron for this purpose. See [Ordnance, Construction of].
Wrought and cast iron are much used in this way for cannon in both the United States and in England. In the former, all the larger cannon belonging to the official system (both siege and sea-coast) are made of the cast metal, whereas the Parrott gun and the new rifled pieces are a combination of both. (See [Ordnance, Construction of].) The metal chiefly employed in England is wrought iron, in combination with steel; the largest guns made at the Woolwich Arsenal are of this nature. Bronze, except as modified by the Austrians, has now nearly entirely gone out of use as a cannon metal. In France and the United States, field-pieces, mortars, and howitzers are still made of this material.
Ordnance, Strains Upon. The exterior form of cannon is determined by the variable thickness of the metal which surrounds the bore at different points of its length. In general terms, the thickness is greatest at the seat of the charge, and least at or near the muzzle. This arrangement is made on account of the variable action of the powder and projectile along the bore, and the necessity of disposing the metal in the safest and most economical manner. The pressure at different points may be approximately determined by calculation, or, more accurately, by experiment. In the latter method, the plan generally employed consists in boring a series of small holes through the side of a gun at right angles to its axis at known distances apart. A steel ball is projected from each hole in succession into a target, or ballistic pendulum, by the force of the charge acting through it, and the pressure at the various points is deduced from the velocities communicated to these balls. This method was adopted by Col. Bomford. Instead of the projectile a steel punch may be employed, which is pressed by the force of the charge into a piece of soft copper. (See [Pressure-gauge].) The weight necessary to make an equal indentation in the same piece is then ascertained by a testing machine. The strains to which all fire-arms are subjected may be classified as follows: (1) The tangential strain which tends to split the piece open longitudinally, and is similar in its action to the force which bursts the hoops of a barrel. (2) The longitudinal strain which acts to pull the piece apart in the direction of its length. Its action is greatest at or near the bottom of the bore, and least at the muzzle, where it is nothing; these two strains increase the volume of the metal to which they are applied. (3) A strain of compression which acts from the axis outward to crush the truncated wedges of which a unit of length of the piece may be supposed to consist; this strain compresses the metal and enlarges the bore. (4) A transverse strain which acts to break transversely by bending outward the staves of which the piece may be supposed to consist. This strain compresses the metal on the inner and extends it on the outer surface. It is known that rupture will take place due to the tangential strain alone, when three times the pressure upon a unit of surface of the bore is greater than twice the tensile strength. Due to the longitudinal strain alone, rupture will take place in the direction of the length, when the pressure is greater than twice the tensile strength; and if the transverse strain alone is considered, rupture will take place when twice the pressure is greater than three times the tensile strength. It therefore appears that the tendency to rupture is greater from the action of the tangential force than from any other, and for lengths above two, or perhaps three calibers, the tangential resistance may be said to act alone, as the aid derived from the transverse resistance will be but trifling for greater lengths of bore; but for lengths of bore less than two calibers, this resistance will be aided by both the transverse and the longitudinal resistance. Every piece should therefore have sufficient thickness of breech to prevent splitting through the latter; after this point has been attained, any additional thickness of breech adds nothing to the strength of the piece. It therefore appears that a fire-arm is strongest at or near the bottom of the bore, and that its strength is diminished rapidly as the length of the bore increases to a certain point (probably not more than three calibers from the bottom); after which, for equal thickness of metal, its strength becomes sensibly uniform. The metals of which cannon are made being crystalline in structure, the size and arrangement of the crystals have an important influence on its strength to resist a particular force; and a metal will have the greatest strength with reference to a particular force when its crystals are small, and the principal faces are parallel to the straining force, if it be one of extension, and perpendicular to it, if it be one of compression. The position of the principal crystalline faces of a cooling solid is found to be perpendicular to the cooling surface; the result of this arrangement of crystals is to create planes of weakness where the different systems of crystals intersect. The effect of this law upon cannons, it has been discovered, is to render radial specimens more tenacious than those cut tangentially from the same gun. The manner and rapidity of cooling have also a great effect upon the ability of cannon to resist strains, and as all solid bodies contract their size in the operation of cooling, it follows that if the different parts of a cannon cool unequally, it will change its form, provided it be not restrained by the presence of a superior force. If it be so restrained, the contractile force will diminish the adhesion of the parts by an amount which depends on the rate of cooling of the different parts, and the contractibility of the metal. This is an important consideration in estimating the strength and endurance of cannon, particularly those made of cast iron. All such cannon cooled from the exterior (see [Ordnance, Construction of]) are affected by two straining forces; the outer portion of the metal being compressed, and the interior extended, in proportion to their distances from the neutral axis or line composed of particles which are neither extended nor compressed by the cooling process. The effect of this unequal contraction may be so great as to crack the interior metal of cast iron even before it has been subjected to the force of gunpowder. The strain produced by the explosion of gunpowder is not distributed equally over the thickness of metal, but it varies inversely as the square of the distance from the centre; it therefore follows that the sides of a cannon are not rent asunder as by a simple tensile force, but they are torn apart like a piece of cloth, commencing at the surface of the bore. Hence it is that the effect of ordinary cooling is to diminish the strength and hardness of the metal of cannon at or near a point where the greatest strength and hardness are required, i.e., at the surface of the bore. The strains produced by unequal cooling increase with the diameter of the casting and the irregularity of its form. This explains the great difficulty found in making large cast-iron cannon proportionally as strong as small ones, and also how projections like bands, moldings, etc., injure the strength of cannon. It also explains why cannon made of “light” cast iron, or cast iron made more tenacious by partial decarbonization, are not so strong as cannon made of weaker iron; for it is well known that such iron contracts more than the latter in cooling, and therefore produces a greater strain of extension on the surface of the bore. Capt. Rodman of the U. S. Ordnance Department has proposed a plan for cooling cannon from the interior (see [Ordnance, Construction of]), thereby reversing the strains produced by external cooling, and making them contribute to the endurance rather than to the injury of the piece. It is likely, however, that the strains produced by unequal cooling are modified by time, which probably allows the particles to accommodate themselves to a certain extent to their constrained position. In confirmation of this, great endurance has been frequently found in old solid cast guns, as in the old 42-pounders tested about the beginning of the war, 1861-65.
Ordnance Department. In the United States, was first established May 14, 1812, and was not provided for in the reduction of the army in 1815, but continued in the service. In 1821 the department was merged into the artillery, attaching to each regiment of artillery 1 supernumerary captain, and giving to each company 4 subaltern officers. The corps of ordnance was re-established April 5, 1832. The department consists of 1 brigadier-general, 3 colonels, 4 lieutenant-colonels, 10 majors, 20 captains, 16 first lieutenants, and 350 enlisted men. It is the duty of the senior officer of the ordnance department to direct the inspection and proving of all pieces of ordnance, shot, shells, small-arms, and equipments procured for the use of the armies of the United States; and to direct the construction of all cannon and carriages, and every implement and apparatus for ordnance, and all ammunition-wagons, traveling-forges, and artificers’ wagons; the inspection and proving of powder, and the preparation of all kinds of ammunition and ordnance stores. It is also the duty of the senior officer of the ordnance department to furnish estimates, and, under the direction of the Secretary of War, to make contracts and purchases for procuring the necessary supplies of arms, ordnance, and ordnance stores, etc. In the British service, the ordnance department was a distinct branch of the war department, originally for the supply of all warlike stores used in the naval or military service. The first master of ordnance was created in the time of Henry VIII., and the Tower of London was probably the depot of arms and military stores; Robert, earl of Essex, is said to have been the first master-general, in 1596. It does not appear that the ordnance department of the British service became especially military until the early part of the 18th century, after the organization of the Royal Artillery, in 1743, under the Duke of Montague as master-general. From this time the ordnance department was administered by a master-general and board, the latter being composed of a lieutenant-general of ordnance, surveyor-general, clerk of the ordnance, principal store-keeper, clerk of the deliveries, and treasurer. About 1763 the department became a construction board, with charge of all forts and fortresses, and directed the construction of all the fortifications and military store-houses, and barracks for the ordnance corps. The board was finally abolished as a separate department, the duties carried on by the commander-in-chief, and the various civil branches by separate offices under the secretary of state for war.
Ordnance Office. Before the invention of guns, this office was supplied by officers under the following names: the bowyer, the cross-bowyer, the galeater, or purveyor of helmets, the armorer, and the keeper of the tents. Henry VIII. placed under the management of a master-general, a lieutenant, surveyor, etc. The master-general was chosen from among the first generals in the service of the sovereign. The appointment was formerly for life; but since the restoration, was held durante bene placito, and not unfrequently by a cabinet minister. The letters patent for this office were revoked May 25, 1855, and its duties vested in the minister of war. The last master-general was Lord Fitzroy Somerset, afterwards Lord Raglan.
Ordnance Projectile. See [Projectile].
Ordnance Sergeants. In the U. S. service, are staff sergeants who are selected from the sergeants of the line of the army. Their duties consist in receiving and preserving the ordnance, arms, ammunition, and other ordnance stores at posts, under the direction of the commanding officer of the same. They must not be confounded with sergeants of ordnance, who are sergeants in the ordnance detachments at arsenals, etc.
Ordnance Store-keeper. In the British service, is a civil officer in the artillery who has charge of all the stores, for which he is accountable to the office of ordnance.