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diff --git a/33535-8.txt b/33535-8.txt new file mode 100644 index 0000000..6f7805a --- /dev/null +++ b/33535-8.txt @@ -0,0 +1,1417 @@ +The Project Gutenberg EBook of The Development of Armor-piercing Shells, by +Carlos de Zafra + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: The Development of Armor-piercing Shells + with Suggestions for their Improvement + +Author: Carlos de Zafra + +Release Date: August 25, 2010 [EBook #33535] + +Language: English + +Character set encoding: ISO-8859-1 + +*** START OF THIS PROJECT GUTENBERG EBOOK DEVELOPMENT OF ARMOR-PIERCING SHELLS *** + + + + +Produced by The Online Distributed Proofreading Team at +https://www.pgdp.net + + + + + + +THE DEVELOPMENT OF + +Armor-piercing Shells + +(With Suggestions for their Improvement) + + + +By + +CARLOS DE ZAFRA, M.E. + +Faculty Lecturer, New York University + + + +1915 + + + + +Historical + + +The manufacture of projectiles to meet the requirements of the modern +science of warfare has been brought to its present high stage of +development through a long series of experiments based, at first, more +upon theory than perhaps any other branch of engineering. + +In the days of wooden vessels very little thought was given to the +actual _physical_ properties of the then cast iron spherical mass. +The gun was the agent upon which depended the ability of the projectile +to penetrate. The projectile, being confronted by so slight a resisting +material as wood, was distorted or physically affected to practically +no degree by the resisting medium. When fighting yard-arm to yard-arm +the power of the gun was sufficient to fully penetrate the enemy, while +at long ranges considerable damage would be executed without in the +least impairing, by the shock of impact (which was inconsiderable as +compared with modern conditions) the physical condition of the shot. + +In the days of the all-wood vessel the guns were of the smooth-bore +class divided into various types with nomenclature according to the +size or weight of the shot, very much as they are today, i.e., +3-pounder, 6-pounder, 4-inch, 10-inch, etc. + +A general review of the gradual development of projectiles will be +found beneficial and helpful to a more complete understanding of the +complexities involved in overcoming the present day difficulties. + +In the smooth-bore gun spherical shot was used. This was by no means a +tight fitting device. Upon firing the gun considerable powder pressure +was lost through the rapid escape of the gases past the shot between it +and the bore of the gun. This would most naturally be expected since at +best the surface of contact between the shot and the bore would be only +a circular line quickly eliminated or worn away through friction under +the high temperature of the burning gases behind the shot. The most +obvious way to eliminate that wearing away of the bearing surface was +to increase it, in doing which the escape of gas past the projectile +would be greatly checked, and the gas pressure behind the projectile +increased (exerting, thereby, a greater propelling force) and imparting +to the projectile greater velocity, increased momentum, and consequent +increased penetration. But an increase in the bearing surface of the +shot necessitated an alteration in its shape introducing difficulties +affecting the accuracy of its passage through the air. + +It was not an appreciation of any ineffectiveness in the early shot +that first brought about a realization of the importance of obtaining +the highest possible results from the material at hand, for no +difficulty was experienced in penetrating the early wooden barriers. +But with the introduction of rail-road and boiler iron and anchor +chains along the sides of the vessels of war as a protection it was +demonstrated that the old round shot previously most effective at the +same range was now of little consequence. Armored vessels, though crude +as was their armor, could with impunity run up along side a wooden +enemy and demand immediate surrender with immediate destruction as the +penalty for non-compliance. It is only necessary to refer to the Naval +History of the Civil War of the United States for the most convincing +proof that this was so. + +Thus began one of the greatest industrial wars of the World--the Battle +of Guns and Armor, which has been constantly waged through years of +international peace and prosperity, and is destined to continue +indefinitely or until the Utopian days of Universal Disarmament and +everlasting peace arrive. + + + + +Early Developments + + +With the change from the spherical to the longitudinal projectile, +difficulties in securing accuracy of flight arose not previously +existing. It was found that the elongated projectile would tumble or +revolve about its transverse axis during its flight, also wobble or +describe a cork screw or spiral trajectory--capital defects requiring +immediate attention. + +The principle of the gyroscope to the effect that a body would maintain +any desired position while revolving at a high rate about the proper +axis was known and it was found desirable to adopt this principle in +some practical manner to the development and improvement of the +projectile. It was believed that were it possible to give a high +rotative speed to the projectile about its major axis the desired +object of keeping that axis co-incident with the vertical plane of the +trajectory would be accomplished. + +Among the first steps towards the development of the modern rifled +artillery and elongated projectile we find certain improvements to have +originated in the small arms pieces. In his "Report on the Art of War +in Europe in 1854, 1855, and 1856" Colonel R. Delafield, U.S.A., +gives the first reference of immediate importance to the subject in +question. The small arms bullet was of lead which readily adapted +itself to such configuration as was desired. Great contrariety of +opinion existed as to the best form of ball and principle, even, by +which it was caused to partake of the rifle twist of the gun barrel. +The following are some of the first forms and methods adopted and are +worthy of consideration: + +[Illustration: Fig. 1] + +Among the French and some others the "tige principle" was employed. It +consisted in forcing the base of the ball open so "as to fit the bore +and rifle grooves by driving it on a projecting spike in the bottom of +the gun attached to the breech, and rising through the charge of +powder," as in Fig. 1. For this purpose a countersunk rammer head to +fit over the head of the ball had to be used. + +[Illustration: Fig. 2 + +Fig. 3 + +Fig. 4 + +Fig. 5 + +Fig. 6 + +Fig. 7] + +In the English Enfield rifle a form of ball was used consisting of a +hollow cup or cone in the bored-out base of the ball (Figs. 2 and 3) +the action of the powder driving this cup into the ball causing it to +expand and take the rifling. Iron cups were used in the Crimea but +because of occasionally cutting off and leaving in the bore a ring of +lead were discarded for solid wood or papier maché cups (Fig. 4). Figs. +5 and 6 show forms of hollow base balls used by the French and +Russians, in which the direct action of the powder on the base caused +the sought for expansion into the rifling. + +The Russians at Sebastopol employed also a fourth principle consisting +of two short projections or lugs on the cylindrical part of the solid +ball to engage in two grooves cut in the bore of the gun. Its +proportions are illustrated by Fig. 7. + +[Illustration: Fig. 8 + +Fig. 9 + +Fig. 10 + +Fig. 11 + +Fig. 12 + +Fig. 13] + +The modifications of the preceding forms, shown in Figs. 8 and 9 were +used in the Crimea by the Sardinian army which also used a smoothbore +musket with solid ball as per Fig. 10. The French army Zouaves used a +solid cylindro-conical grooved ball, as in Fig. 11, in a tige rifle. + +The 1856 Austrian rifle used a solid cylindro-conical ball, "with two +deep grooves cut in the cylindrical part such that the parts between +the grooves are forced together and outwards, or upset by the explosion +of the powder, to fill the bore and the rifle grooves," as in Fig. 12. +Fig. 13 illustrates the same principle as used by the Saxon army. + +[Illustration: Fig. 14 + +Fig. 15 + +Fig. 16 + +Fig. 17 + +Fig. 18] + +Other forms used at the time by the various Powers are illustrated in +Figs. 14, 15, 16, 17, and 18. But it was an open question as to which +was the best form, no Power being fully satisfied. + +It may be noted here that as the breech-loading rifle had not up to +this time been sufficiently perfected, all the above bullets were for +muzzle loading rifles. Breech-loading arms had been known for over two +centuries but were as yet unreliable, clumsy, and generally imperfect. + +[Illustration: Fig. 19. The Lancaster Gun.] + +The early methods adopted in the construction of cannon to impart to +the projectile the desired rotary motion are as interesting as the +early methods adopted in the construction of the projectile. Heavy +rifled artillery was introduced in 1856 against Cronstadt. The English +artillery at Sebastopol used the Lancaster Gun, illustrated in Fig. 19. +The form of the bore section of this gun was that of an ellipse of 8" +and 8-5/8" diameters, the bore being generated by the section of such +an elipse making a revolution of about one-quarter turn in the length +of the bore, the center of the section always co-incident with the +longitudinal axis of the gun, forming thereby a continuous elliptical +cylinder, the greater axis at the muzzle lying in the vertical plane +and gradually becoming horizontal at the breech section, or in other +words, the whole length and section of the bore was a rifle twist of +one quarter of a turn in its length. + +The projectile was a wrought iron shell of the form and size indicated +in Fig. 20, as ascertained by measurement of one found in the trenches +at Sebastopol. + +[Illustration: Fig. 20] + +The use of these guns in the siege was by no means satisfactory, giving +neither precision of fire nor extraordinary range, while the gun more +often failed by bursting than other types. The principle, however, met +with favor and was studied and improved upon. + +Another method of applying the rifle principle to heavy guns consisted +in casting a segment of a sphere (nearly) on the side of the cylinder +part of the shot with corresponding grooves in the bore of the gun, +making about one turn in twenty feet. It is somewhat like the principle +of the solid musket ball, Fig. 7 with a difference in the shape of the +projections, as shown in the annexed Fig. 21, giving the form and size +(nearly) of the shot. + +Guns of this pattern were adopted for many of the gunboats fitted out +by France for operations in the Baltic in 1856, some with four and +others with two guns each. + +[Illustration: Fig. 21] + +[Illustration: Fig. 22] + +The bore of the gun had a circular section of 6-1/2" diameter with two +grooves cut in it, as shown in Fig. 22, which in the length of the bore +had a twist equal to one turn in six meters. + +Figures 23 and 24 represent cast iron shot "of very peculiar shape, +intended apparently, as a substitute for the rifle groove. They were +cylinders of about four inches diameter, with a flattened spherical +head from which three spiral openings communicate with the open +interior of the cylinder. The cylindrical part was formed with +grooves...." + +[Illustration: Fig. 23] + +[Illustration: Fig. 24] + + + + +The Modern Type of Gun + + +From these earliest examples the development of artillery has been +gradual until the present day of the built-up gun with an energy and +range undreamed of in the earlier days. The built-up gun of today has +attained to a calibre of 16 inches, a length of nearly 50 feet, a weight +of 124 tons, and an extreme range at 42° elevation of 20.9 miles with a +maximum height of trajectory of over 5-3/4 miles. The projectile, too, +has increased in size from a few pounds to the one ton or 2,240-pound +mass used in the above gun. The energy imparted to it at the muzzle +amounts to 6,408-foot tons assuring a penetration at the muzzle of 33.8 +inches of steel, or at 3,500 yards of 27.5 inches, the muzzle velocity +being 1,975-foot-seconds and powder charge 640 pounds of smokeless. The +maximum pressure in the powder chamber allowed is 37,000 pounds per +square inch. + +Briefly the modern gun is a built-up piece, constructed by fitting or +shrinking super-imposed hoops or cylinders one over the other in size +and number as diagramatically explained in Fig. 25, sufficient to +re-inforce the bore to withstand the varied pressures. + +[Illustration: Fig. 25. 13-inch B.L.R. (Total Length, 40 feet.)] + +[Illustration: Fig. 26] + +The twist or rotary motion is imparted to the projectile by means of +the "rifling" in the bore. Fig. 26 shows the cross-section of an 8-inch +gun with the dimensions of the rifling, which is composed of two +elements, the "groove" or spiral cut made in the bore and the "land" or +space between two adjacent grooves. To take these grooves "rotating +bands" of soft metal, generally copper, are fitted to the projectile as +will be explained under "Manufacture of Projectiles." + + + + +Classification of Projectiles + + +Projectiles are classified according to their calibre, type of gun for +which they are intended, material of which they are made, etc., as +per the following scheme used in the U.S. Army for marking cases of +projectiles: + + { Cast steel + Inch { Rifle { Cast iron + { Mortar { Common steel { Shot + { Armor piercing { Shell + { Rendable A.P. + Weight empty--Lbs. + Capped or uncapped + or + Capped and grooved for base cover + or + Uncapped and grooved for base cover + Base } Fuze + Point } + + + + +Manufacture of Projectiles + + +While a high state of development has been attained in the manufacture +of armor-piercing shells attention will be confined to their +manufacture in so much as the methods for improvement hereinafter +suggested are intended to affect the physical and not the chemical +properties of the material, and are, therefore, applicable to all +projectiles in which the stresses to be resisted exceed the resisting +powers of the projectiles as at present manufactured. + +The function to be performed by an armor-piercing shell is that of +fully penetrating, without disruption to itself, an armor plate in +thickness equal to, at least, the calibre of the shell in question, and +then be in condition for effective bursting. + +The following extracts from the Army and Navy specifications pertain +to: + + +MATERIAL AND WORKMANSHIP + +(Art 20, O. D., U.S.A.) + +The projectiles must be of forged steel, sound, and _free from cracks, +seams, and other defects_[1]. + + [1] _Italics_ are those of the author and refer to defects which + it is the object of his design and method of manufacture to + remedy. + +The base plugs must be of forged steel, annealed after forging or +tempering, free from seams, cracks, and other defects, and have the +following physical properties: + + Elastic limit 50,000 to 60,000 pounds + Tensile strength 90,000 to 100,000 " + Elongation 18 per cent. + Contraction 25 " " + +The projectiles shall be machine-finished, before treatment, as close +to the prescribed dimensions as may be consistent with that operation, +and must, if necessary, be finally finished to the prescribed +dimensions within the allowed variations. + +Cylindrical tensile-test specimens with diameter of stem of 0.505 inch +will be used in all cases when the piece is sufficiently thick to +finish the stem to that dimension; when not, the inspectors will +determine the exact form or diameter of the specimens to be used, the +largest practicable being used, considering the piece under test. A +length of stem between gauge marks of 2 inches will be used in all +cases where the elongation is to be taken. + + +CAPPING + +(Art. 21, O. D., U.S.A.) + +All steel projectiles shall be fitted, when required, with a cap of +soft steel placed upon the point,[2] the caps to be of the dimensions +shown on the approved drawings and secured in a manner satisfactory to +the Chief of Ordnance by means of a groove, to be turned on the head of +the projectile prior to tempering. + + [2] See Frontispiece. + +The steel for the cap must show a tensile strength not to exceed 60,000 +pounds per square inch, an elongation after rupture of not less than 30 +per cent, and a reduction in area of not less than 45 per cent on +standard specimens, 2 inches long between measuring points and 0.505 +inch in diameter. These caps will be thoroughly annealed before being +placed upon the projectiles and will be free from cracks and all other +defects. + + +TEST FOR DETECTION OF HOLES, CRACKS, ETC. + +(Art. 27, O. D., U.S.A.) + +After the submission of a lot to the inspector for selection of samples +for ballistic test, and before final delivery, the projectiles must be +subjected to an interior hydraulic pressure of 500 pounds per square +inch for one minute. All projectiles in which _holes_, _cracks_, _or +any unsoundness_ are developed by this test will be rejected. + + +TENSILE TEST + +(Art. 28, O. D., U.S.A.) + +After forging, the projectiles shall be annealed at a temperature of at +least 1,200° F.; and after being annealed, tangential test specimens +shall be taken from the base or base prolonged of 2 per cent of the +projectiles from each lot selected at random by the inspector. + +The tensile strength of the projectiles in a lot shall not vary more +than 20,000 pounds from the highest to the lowest. + + +CHEMICAL TEST + +(Art. 30, O. D., U.S.A.) + +A careful and complete chemical analysis shall be made of the metal of +each heat from which the projectiles are manufactured under these +specifications. + + +TESTS FOR THE DETECTION OF INITIAL STRAINS BORDERING ON RUPTURE + +(Art. 31, O. D., U.S.A.) + +After final treatment and before acceptance for the ballistic test, all +A.P. shot must be cooled to a temperature of about 40° F., and then +suddenly heated by being plunged into a bath of water at a temperature +of from 180° F. to 212° F., as the Chief of Ordnance may direct. When +thoroughly heated to this temperature each projectile must be plunged, +with its axis horizontal, halfway into a bath of water at a temperature +not greater than 40° F., and after a brief period shall be turned 180° +for a like immersion of the opposite side, after which the projectile +shall be removed from the bath. + +This test shall be made in the presence of the inspector, and an +interval of at least three days must elapse between the final treatment +and the submission of the projectiles to this test. This test is not +required for shell. + + +BALLISTIC TEST + +(Art. 32, O. D., U.S.A.) + +Each lot of projectiles shall be subjected to the following ballistic +test: + +After a final treatment and on presentation of the entire lot for +the ballistic test, the inspector shall select three projectiles to +represent the lot, which shall be finished, inspected and delivered +in the same manner as required for the rest of the lot. + +(a) Armor-piercing shot. Two capped shot, sandloaded to standard +weight, shall be fired against a hard-faced Krupp armor plate from 1 +to 1-1/2 calibres thick, secured to a timber backing in a manner +satisfactory to the Chief of Ordnance, with about the corresponding +velocity given by the following table, with the requirement that the +shot shall perforate the plate unbroken and then be in condition for +effective bursting. + +If both projectiles fulfill the above test, the lot will be accepted. + +If, one of the shots fails to pass the test here prescribed, a +supplementary test shall be made by firing the third shot under the +same conditions as the first two shot; if this passes the test as +prescribed above, the lot shall be accepted; if it fails to do this, +the lot shall not be accepted. + + --------------+-------------+----------------+------------- + Calibre of | Weight of | Thickness of | Velocity for + shot | shot | plate | penetration + --------------+-------------+----------------+------------- + 4-inch | 33[3] | { 4-inch | 1,930 + | | { 5-inch | 2,295 + | | | + 4.7-inch | 45[3] | 5-inch | 2,220 + | | | + 5-inch | 58 | { 5-inch | 2,005 + | | { 6-inch | 2,320 + | | | + 6-inch | 106 | { 6-inch | 1,950 + | | { 8-inch | 2,450 + | | | + 8-inch | 316 | { 8-inch | 1,760 + | | { 10-inch | 2,100 + | | | + 10-inch | 604 | { 10-inch | 1,745 + | | { 12-inch | 2,020 + | | | + 12-inch | 1,046 | 12-inch | 1,730 + --------------+-------------+----------------+------------- + + [3] Weight uncapped. + +For intermediate thickness the velocity shall be determined by +interpolation. + +(b) Armor-piercing shell. Two capped shell, sandloaded to standard +weight, shall be fired against a hard-faced Harveyized armor plate +secure to a timber backing in a manner satisfactory to the Chief of +Ordnance, of 3-inches thickness for 5-inch and 6-inch shell, 4-inches +for 8-inch shell, 5-inches for 10-inch shell, and 6-inches for 12-inch +shell, with a velocity[4] of about 1,420 f.s. for the 5-inch shell, +1,220 f.s. for the 6-inch shell and 920 f.s. for the 8-inch, 10-inch +and 12-inch shell at impact, with the requirement that the shell shall +go through the plate unbroken, and then be in a condition for effective +bursting. + + [4] The weight of powder charge to give the prescribed velocity + will be determined shortly before the test, cast iron projectiles + of proper weight being fired for the purpose; this weight of + charge will be taken as giving the prescribed velocity to the + projectiles undergoing test. + + * * * * * + +(c) 12-inch deck piercing shell. Two shell, sandfilled to standard +weight, will be fired with a striking velocity sufficient to pass +completely through a 4-1/2-inch nickel-steel protective-deck plate +inclined so as to give an angle of impact of 60 degrees, and to be +supported by a suitable backing of wood; or both shell shall be +subjected to such alternate ballistic test as the Department may judge +to be an equivalent to the above in its effect upon the projectile. + + * * * * * + +The nickel-steel protective-deck plate shall be manufactured by the +open-hearth process and shall contain about 3-1/4 per cent of nickel, +not more than six one-hundredths of one per cent of phosphorous; not +more than four one-hundredths of one per cent of sulphur, shall be the +best composition in all respects. + +It shall be oil or water tempered and annealed, and the whole plate +shall be subjected to the same treatment at the same time. + +Tensile test will be made after final treatment. One longitudinal +specimen for tensile test will be taken from each plate. Each shall +show a tensile strength of at least 80,000 pounds per square inch and +an elongation in 2 inches of at least 27 per cent. + +Bending tests will be made as follows: A piece cut from the plate shall +be doubled cold around a curve of which the diameter is not more than +the thickness of the piece tested without showing any cracks. The ends +of the piece are to be parallel after bending. These specimens shall be +12 inches long, 1-1/2 inches wide, and 1 inch thick. + +At the discretion of the inspector, bending specimens 1/2 inch square +taken with a hollow drill, may be substituted. Such specimens must bend +cold to 180 degrees flat, without sign of fracture on outer surface. + +(d) 12-inch Torpedo Shell. Two shell, sandloaded to standard weight, +will be fired from a gun or mortar into a sand butt with a pressure in +the powder chamber of about 37,000 pounds per square inch to test +structural ability. + +If the shell are found not seriously deformed by discharge from the +piece and in a condition for effective bursting, the lot will be +accepted. + +If any of the shell fail to pass this test, the lot will be rejected. + +The following extract from the "Circulars and Specifications of the +Navy Department concerning Armor Plate and Appurtenances for Vessels of +the U.S. Navy," (April 22, 1907) while pertaining to another subject, +will be pardoned if introduced here for the purpose of demonstrating +the seemingly paradoxical requirements a manufacturer is called upon to +meet: + +(Par. 60.) The ballistic test for acceptance of armor shall be made as +strictly as practicable in accordance with the following tables, the +Department reserving the right to use guns of other calibres than +designated for any plate if it is deemed advisable. + +In the test of armor of Class A there shall be three impacts with +striking velocities as given in the following table, capped +armor-piercing projectiles being used: + + -------------+-----------+-------------+----------- + Wt. of shell| Calibre of| Thickness of| Striking + capped | gun | plates | velocity + Pounds | Inches | Inches |Ft.-seconds + -------------+-----------+-------------+----------- + 105 | 6 | 5 | 1,451 + 105 | 6 | 6 | 1,648 + 105 | 6 | 7 | 1,836 + 165 | 7 | 6 | 1,464 + 165 | 7 | 7 | 1,631 + 165 | 7 | 8 | 1,791 + 260 | 8 | 7 | 1,459 + 260 | 8 | 8 | 1,603 + 260 | 8 | 9 | 1,741 + 510 | 10 | 9 | 1,458 + 510 | 10 | 10 | 1,568 + 510 | 10 | 11 | 1,676 + 870 | 12 | 11 | 1,424 + 870 | 12 | 12 | 1,514 + -------------+-----------+-------------+----------- + +The first impact shall be located near the central portion of the +plate, and the other two impacts shall be located as directed by the +Bureau; no impact, however, to be nearer another impact or an edge of +the plate than 3-1/2 calibres of the projectile used. + +On these three impacts no projectile or fragment thereof shall get +entirely through the plate and backing, nor shall any through crack +develop to an edge of the plate or to another impact. + + * * * * * + +From the above it is seen that a manufacturer supplying both +armor-plate and shell to the Government is called upon to produce a +shell with sufficient integrity to completely penetrate, and without +breaking up, his armor-plate of sufficient thickness to resist that +shell. + +The capping of projectiles consists in placing over the point a cone or +mass of metal of comparative softness. In the United States services +soft steel is used for the purpose. Authorities disagree as to the +exact function which the cap plays, some claiming it to act as a +lubricating metal facilitating the passage of the projectile, others +claim that it gives an initial shock to the armor-plate before the +shell proper has struck it, which latter then strikes the plate in a +state of molecular unrest, and, therefore, of impaired resisting power. +Firing tests of shell at armor-plate at oblique angles have proven the +capped shell superior, which would indicate that the cap in this +instance at any rate is capable of securing a hold on the plate which +the bare point of the shell cannot, in so much as uncapped shells +glance off. At any rate capped projectiles are, on the whole, superior +to the uncapped and the practice of capping is recommended as an +additional advantage when used in conjunction with the improvements +here-in-after described. + +At a specified distance from the base of the shell a groove or +band-score is turned for the rotation band. For projectiles under +7-inches calibre, pure copper is usually employed, but for larger +calibre an alloy of 97-1/2 per cent of pure copper and 2-1/2 per cent +of nickel is used and is annealed before banding. The rough bands are +in a form of solid rings cut from drawn tubes or cylindrical castings, +and must be carefully hammered into the score or preferably pressed in +by hydraulic pressure and finally turned to proper size, shape, and +finish. + +Their use has been previously described and the improvements in +armor-piercing shells hereinafter described are based upon a study of +the stresses sustained by a projectile upon impact while rotating about +its major axis at the high rotative velocity which the engaging of +these bands with the rifling of the gun has imparted to the shell. + +The following table compiled by the author gives the rotative +velocities of various projectiles: + + -------+----------+----------+-------+-------+------+------------ + | | | | | Muz. | + | | | | | Engy.| + Calibre|Wt., lbs. | Muz. Vel.| | | Ft. | Type of + Inches |Projectile| Ft. Secs.| R.P.S.| R.P.M.| Tons | Gun + -------+----------+----------+-------+-------+------+------------ + 3 | 12 | 870 | 139 | 8,340| 63 |Hotchkiss + 3.2 | 13.5 | 1,685 | 253 | 15,180| 266 |Field '90 + 3.6 | 20 | 1,550 | 206 | 12,360| 333 | " 1891 + 3.6 | 20 | 650 | 86 | 5,160| 59 |Mortar 1890 + 5 | 45 | 1,830 | 176 | 9,560|1,045 |Siege 1890 + 7 | 105 | 1,085 | 76 | 4,560| 853 |Howitzer '90 + 7 | 125 | 690 | 49 | 2,940| 412 |Mortar '92 + -------+----------+----------+-------+-------+------+------------ + + U.S. SEA-COAST LAND SERVICE GUNS + + -------+----------+----------+-------+-------+--------+---------- + | | | | | Muz. | + | | | | | Engy. | + Calibre|Wt., lbs. | Muz. Vel.| | | Ft. | Type of + Inches |Projectile| Ft. Secs.| R.P.S.| R.P.M.| Tons | Gun + -------+----------+----------+-------+-------+--------+---------- + 8 | 300 | 1,950 | 111 | 6,660 | 7,907 | 1888M + 10 | 575 | 1,975 | 95 | 5,700 | 15,548 | 1888M + 12 | 1,000 | 2,100 | 84 | 5,040 | 30,750 | 1902 + 16 | 2,370 | 1,975 | 59 | 3,540 | 64,084 | + -------+----------+----------+-------+-------+--------+---------- + + KRUPP GUNS + + -------+----------+----------+-------+--------+-------+---------- + | | | | | Muz. | + | | | | | Engy. | + Calibre|Wt., lbs. | Muz. Vel.| | | Ft. | Type of + Inches |Projectile| Ft. Secs.| R.P.S.| R.P.M. | Tons | Gun + -------+----------+----------+-------+--------+-------+---------- + 6 | | 2,600 | 192 | 15,520 | | + | | 3,000 | 222 | 13,320 | | + 8 | | 2,200 | 133 | 7,980 | | + 10 | | 2,250 | 108 | 6,480 | | + 12 | | 2,250 | 90 | 6,400 | | + -------+----------+----------+-------+--------+-------+---------- + +From the above table it will be noted that the R.P.M. are exceedingly +high in some cases. Upon the impact of a shell with armor-plate the +physical phenomena occur instantaneously and the resultant forces are +so great that it is impossible to mechanically record their action. A +study of the stresses in the shell can, however, be made on a +theoretical basis. + +In the first place, if the projectile were twenty calibres in length +and of a material offering less resistance to torsional stress than +steel and rotated at the high velocities indicated we would find that +upon impact the torsion would be plainly evident as per the following: + +Assume a projectile A of length twenty calibres, about to penetrate an +armor-plate B of thickness sufficient to prevent complete penetration +by the shell in question. + +[Illustration: Fig. 27] + +The tendency of the impact is to stop the rotation of the projectile, +owing to the friction between the surfaces in contact, but owing to the +length of the projectile the point receives this retarding influence +before it can be transmitted throughout the body of the shell to its +base. The consequent result is that the head will finally come to a +stop while the base is still rotating, however slightly that may be. + +Theoretically considering the projectile to be composed of a series of +discs a line drawn parallel to the major axis, while at rest, would be +represented by the line _cd_. Upon impact, however, the rotative force +tends to create a twisting couple with the result that each disc will +tend to slide on its preceding disc, so that by the time these twisting +couples have been transmitted to the base of the shell the original +line _cd_ will have taken some such position as _de_. + +The objection to the present method of forging shells is as a result, +the grain or fibre of the metal lies parallel with the major axis of +the forging, the forging process causing an elongation of the ingot and +the metal grain following the direction of elongation. Consequently any +flaws occurring in the material will extend parallel to the grain or +major axis. If a flaw remains undiscovered in a finished projectile--as +is sometimes the case--the projectile is not only weakened thereby, but +the element of weakness lies in such a direction that the compression +forces and counterforces produce very much the same results as would a +wedge driven into a niche, i.e. the separation of adjacent material. +The author is in possession of a shell in which a longitudinal flaw was +revealed in the ogive by the cutting away of a longitudinal quarter +section, Fig. 28. + +[Illustration: Fig. 28. Armor-Piercing Shell. Showing position of +flaw.] + +There are, therefore, two great forces with which to contend in the +design of projectiles, to one of which, compression, has been given the +greatest attention because of its recognized tendency to cause the base +of the shell to crowd upon the head and cause the shell to break up +about the ogive. The other force, torsion, seems not to have been +considered prior to the present instance, at any rate so far as the +author has been able to ascertain, not because thought to be +unimportant, but because of oversight or failure on the part of +investigators to take into consideration in this instance, an element +of reaction commonly considered in mechanical engineering practice, as +in shafting for vessels and for power transmission in shops, etc. + +The writer maintains that immediately upon impact the metal in a shell +assumes a state of physical unrest, due to stresses similar to those in +a propeller shaft when in motion, except that in the former case the +intensity of the compression stresses greatly exceed those in the +latter. Because a shell is only 3-1/2 calibres in length is no +criterion that the same stresses do not exist there as would exist in +the theoretical projectile considered of twenty calibres, or one of +even more exaggerated proportions--there would be merely a difference +in the _intensity_ of these stresses. + +In a projectile making one complete revolution about its major axis in +every twenty-five calibres flight, any one elementary unit area or mass +in that shell likewise makes one complete revolution in the same +distance of travel, and the path traversed by that unit area or mass is +that of a spiral of radius equal to the distance of that unit area or +mass from the major axis of the shell, the diameter of which spiral +would be the diameter of the shell in question--and the pitch +twenty-five calibres--if said unit area were on the surface of the body +of the shell. + +Upon impact the tendency of this unit area would be to continue its +flight along the continuation of that spiral or along the line _ed_ +of our theoretical shell of twenty calibres. The result would be for +each disc element theoretically considered to crowd upon the next +corresponding disc element and these two upon the third corresponding +disc element etc., such crowding taking place along the line _ed_. +Therefore the projectile must be designed not only to penetrate, as +well as to withstand the great compressional stresses upon the +advancing head of the shell but the body of the shell must be so +designed as to give a maximum of integrity. The torsional stresses act +along _ed_, and in order to resist these stresses the shell must be so +designed that the resisting ability will be increased along that line, +re-acting along _de_. + +This the author advocates by means of a "twist forging," in which the +grain of the metal will lie co-incident with the lines of the torsional +stresses, and by the introduction of spiral ribs lying co-incident also +with the lines of the torsional stresses and the grain of the "twist +forging" manufactured by a process indicated in the patent herewith +appended. By the introduction of the spiral ribs it will be seen that +each disc is reinforced to withstand the tendency of the disc behind to +crowd upon it and that by means of a properly designed shell of this +type the whole energy of the shell can be better transmitted to the +point of impact by means of the spiral ribs and twisted grain. + +Furthermore, should any flaws be present in the ingot, their size would +be reduced by the twisting, as are the spaces between the strands of a +rope when twisted in the proper direction for so doing. Also, with a +flaw in a finished projectile, and lying in a spiral direction the +result of the compression stresses would be to jump across the flaw or +to decrease the gap instead of acting wedgelike along the flaw causing +it to open as before mentioned. Finally, an increase in integrity means +an increase in penetrability, or in the percentage of complete +penetration, with the ultimate necessity of increasing the thickness of +armor-plate to successfully exclude the improved armor-piercing shell. + + + No. 863,248. PATENTED AUG. 13, 1907. + + C. DE ZAFRA. + + PROJECTILE. + + APPLICATION FILED DEC. 10, 1906. + + [Illustration: FIG. 1.] + + [Illustration: FIG. 2.] + + [Illustration: FIG. 3.] + + [Illustration: Witnesses + [Names are illegible] + + Carlos de Zafra Inventor + + By his Attorney Hensey Gough + + + + +United States Patent Office + +CARLOS DE ZAFRA, OF NEW YORK, N.Y. + +Projectile + + +No. 863,248 + +SPECIFICATION OF LETTERS PATENT. Patented Aug. 13, 1907. + +Application filed December 10, 1906, Serial No. 347,055 + + +_To all whom it may concern:_ + +Be it known that I, CARLOS DE ZAFRA, a citizen of the United States, +residing at New York city, county of New York, and State of New York, +have invented certain new and useful Improvements in Projectiles, of +which the following is a specification. + +My invention, relates to an improved form of explosive shell or other +projectile, and more particularly to those projectiles which are +reinforced by longitudinal ribs. + +It further relates to a method whereby such a projectile may be made. + +The object of my invention is to provide a shell having a maximum +strength or perforating power, together with a maximum capacity for an +explosive charge, and the invention consists in forming the projectile +with the fibers or grain of the metal running in a spiral direction +from the base of the shell to the top thereof, and in reinforcing the +interior of the shell with ribs which shall run in the same direction, +starting at the base of the projectile and ending at the top end of the +inner chamber. + +In the drawings, Figure 1 is a side view of a projectile, the grain or +fiber of which is indicated by dotted lines. Fig. 2 is a longitudinal +section showing the interior ribs. Fig. 3 is a transverse section on +the line 3--3, Fig. 2. + +While the tendency to rupture is very much lessened by the use of +straight longitudinal ribs on the interior of shells and projectiles of +various kinds, yet such a straight longitudinal rib is itself liable to +a sheering and disruptive stress along transverse lines when the +projectile strikes, due to the rotative inertia of the projectile in +its flight. + +The aim of my invention is to provide ribs which will be coincident +with the rotative travel of the shell so that when the point of the +projectile enters an armor plate, the stress of this sudden stoppage of +rotation will be taken up along the fiber or grain of the shell and by +the spiral ribs therein. Thus the sheering tendency of the metal in the +walls of the shell is greatly reduced and greater strength is given to +resist the tendency of the rear end of the shell to twist off, due to +the rotatory course when the head of the shell is embedded in an armor +plate. + +Like letters in the figures designate like parts. + +A represents the shell, and B the fuse, B´ being the rotating band +which is secured on the shell near the base in the usual way. The +hollow portion of the shell consists of a chamber C extending from the +base to the forward end of the shell. The walls of this chamber are +provided with the ribs D extending from the base to the point of the +chamber in a spiral direction. In the drawings, I have shown the pitch +of this spiral as one quarter turn in the length of the chamber, but it +is to be understood that I may use a greater or less pitch without +departing in any way from my invention. + +I have shown a pitch of one quarter turn particularly for purposes of +illustration, as if a greater pitch had been used the section Fig. 2 +would not have shown any one rib entirely. + +As will be seen by Fig. 1, the grain or fiber of the metal is also +twisted spirally in accordance with the pitch of the ribs D, in this +case a quarter turn from the rear end of the projectile to its point. + +In order to manufacture a projectile of this character I have devised +the following method which I deem preferable, though I do not wish to +limit myself thereto. This consists first in casting an ingot from +which the solid forging is to be produced. Previous to, during or after +the process of forging, the ingot is twisted in a torsion apparatus, +one end of the ingot being held fixed while the other end is being +rotated by any suitable rotative gripping mechanism through an arc of +the number of degrees desired. This will result in what I term a "twist +forging" in which the grain or fiber will lie in any predetermined or +desired spiral direction or pitch. The spiral ribs which are to lie in +the direction preferably parallel to the grain or fiber of the metal +may now be formed by the boring process similar to that employed in the +rifling of modern artillery. + +My projectile might also be formed by forming the shell with the ribs +running longitudinally there along in a direct line from front to rear +and with the fiber of the metal also running in a direct line parallel +with the ribs. The projectile might then be reheated for forging and +while being forged the rear could be held in any suitable gripping +device and the forward end be rotated, as before explained. Thus the +fiber of the shell and the interior ribs will both be given the spiral +twist desired. + +It will be seen that with either of these processes the fiber of the +shell and the spiral ribs lie parallel to each other and are most +perfectly formed to resist the shock of impact, the reaction of which +will be along the line coincident with the resultant of the angular or +rotative and the trajectoral velocities, which line will lie parallel +with the spiral ribs, the pitch of such fiber and ribs having been +predetermined by suitable calculation. + +The above described methods while not claimed herein are to form the +subject-matter of a separate application. + +Having described my invention what I claim is: + +1. A projectile provided with a chamber extending along its length, the +walls of said chamber being provided with longitudinal ribs extending +in a spiral direction from the base of the chamber to the forward end +thereof. + +2. A projectile provided with a chamber extending along its length, the +forward end of said chamber being pointed, the walls of said chamber +being provided with longitudinal ribs extending in a spiral direction +from the base of the chamber to the point thereof. + +3. A projectile having the fibers of its material twisted in a spiral +direction from the base of said projectile to the end thereof. + +4. A projectile having the fibers of its material twisted in a spiral +direction from the base of said projectile to the end thereof, said +projectile having a central chamber, the walls of which are provided +with longitudinal ribs extending in a spiral direction from the base of +the chamber to the point thereof. + +In testimony whereof, I have signed my name to this specification in +the presence of two subscribing witnesses, this sixth day of December, +1906. + + CARLOS DE ZAFRA. + + Witnesses: + + EMILO BELARI, + EMMA RODERICK. + + + + +Bibliography + + +ORDNANCE AND GUNNERY BRUFF + +TEST BOOK OF ORDNANCE AND GUNNERY INGERSOLL + +REPORT ON THE ART OF WAR IN EUROPE--1854-1855-1856 + COL. R. DELAFIELD, U.S.A. + +JOURNAL OF THE U.S. ARTILLERY + +THE SCIENTIFIC AMERICAN + +SPECIFICATIONS OF THE BUREAU OF ORDNANCE, U.S. NAVY DEPARTMENT + +SPECIFICATIONS OF THE ORDNANCE DEPARTMENT, U.S. ARMY + + +[Illustration: The de Zafra Improved Armor-Piercing Shell] + + + + + + +End of the Project Gutenberg EBook of The Development of Armor-piercing +Shells, by Carlos de Zafra + +*** END OF THIS PROJECT GUTENBERG EBOOK DEVELOPMENT OF ARMOR-PIERCING SHELLS *** + +***** This file should be named 33535-8.txt or 33535-8.zip ***** +This and all associated files of various formats will be found in: + https://www.gutenberg.org/3/3/5/3/33535/ + +Produced by The Online Distributed Proofreading Team at +https://www.pgdp.net + + +Updated editions will replace the previous one--the old editions +will be renamed. + +Creating the works from public domain print editions means that no +one owns a United States copyright in these works, so the Foundation +(and you!) can copy and distribute it in the United States without +permission and without paying copyright royalties. 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