By the Parabolic Theory, the greatest range is when the angle of elevation is 45°, or half a right angle; and the ranges are equal at angles, equally above, and below 45°. In projectiles, moving with velocities not exceeding 300 or 400 feet per second of time, the Parabolic theory will resolve cases tolerably near the truth; but in cases of great projectile velocities, that theory is quite inadequate, without the aid of data, drawn from good experiments; for so great is the effect of the resistance of the air to projectiles of considerable velocity, that some of those, which in the air range only two or three miles, would, in vacuo, range between twenty and thirty miles. The effects of this resistance are also various, according to the velocity, the diameter, and the weight of the shot.
By experiments it will be found that the greatest range (instead of being constantly that at an elevation of 45°, as in the Parabolic theory), will be at all intermediate degrees between 45° and 30° (with ordinary charges about 42°), being more, or less, both according to the velocity, and the weight of the projectile; the smaller velocities, and larger shells ranging farthest when projected almostat an elevationof 45°; while the greatest velocities, especially with the smaller shells, range farthest with an elevation of about 30°. However, as sufficient experiments have not yet been made to establish true rules for practical gunnery, independent of the Parabolic theory, we must at present content ourselves with the data of some one certain experimental range, and time of flight at a given angle of elevation, and then, by help of these, and the Parabolic theory, we can determine the like circumstances for other elevations that are not greatly different from the former, assisted by the following rules:—
PRACTICAL RULES IN GUNNERY.
1.—To find the Velocity of any shot, or shell.
It has been found by experiments, that with shot of mean windage, and powder of mean strength, a charge of one-third of the weight of the ball gives an initial velocity of about 1600 feet per second: therefore,to find the velocity given by any other charge, divide three times the weight of the charge by the weight of the ball, and multiply the square root of the quotient by 1600, the product will be the velocity in feet, or the space the shot passes over in the first second.[28]
2.The first graze, with given elevation, and charge, being known, to determine the charge for any other first graze, and elevation.
Multiply the known charge, and elevation into the proposed first graze, also the proposed elevation into the known first graze, and divide the first product by the last, for the charge required in ounces.
3.Given the range for one charge, to find the range for another charge, or the charge for another range.
The ranges have the same proportion as the charges; that is, as one range is to its charge, so is any other range to its charge, the elevation of the piece being the same in both cases.
Table of Velocities, &c., of shells.
From Experiments on the velocities of shot, the following results have been obtained:—
1.The time of a ball’s flight is nearly as the range, the gun, and elevation being the same.
2.The velocities decrease as the distances increase(arising from the resistance of the air, which opposes the progress of the shot,) in a proportion somewhat higher than the squares of the velocities throughout, and subject only to a small variation.
3.Very little advantage is gained, in point of range, by increasing the chargemore than is necessary to attain the object, the velocities given by large charges being very soon reduced to those by moderate charges; those, for instance, given by half the shot’s weight are reduced to an equality with those by one-third, after passing through a space of only 200 feet. (Vide8.)
4.Very little benefit is derived from increasing the length of guns, the velocity given by long guns of 22 calibres being reduced to an equality with that of short guns of 15½ calibres with similar charges, after passing through the following spaces—viz.:—
5.The resistance of the airagainst balls of different diameters with equal velocities, is very nearly in the proportion of the squares of their diameters, or as their surfaces.
6.A very great increase of velocity may be acquired by a decrease of windage, from ⅓ to ¼ being lost by the windage of ½0 the diameter of the bore.
7.By firing the charge in different parts(separately, or simultaneously), by compressing the charge, by the use of wads, by varying the weight of the gun to lessen the recoil, or even by stopping the recoil entirely, no sensible change is produced in the velocity of the ball.
8.The velocity increases with the charge, to a certain point, peculiar to each gun; but, by further increasing the charge, the velocity gradually diminishes; yet the recoil is always increased by an increase of charge. (Vide3.)
9.The velocities of balls fired with equal chargesincrease to a certain point, when the gun is longer, in a proportion which is nearly the middle ratio between the square and cube roots of the length of the bore.
10.When shot of different weights are fired with the same charges of powder, the velocities communicated to them are nearly in the inverse ratio of the square roots of their weights. Therefore, shot which are of different weights, and impelled by the firing of different charges of powder, acquire velocities which are directly as the square roots of the charges of powder, and inversely as the square roots of the weights of the shot. By making use of shot of a heavier metal than iron (lead for instance) the momentum of the shot discharged with the same charge of powder would be increased in the ratio of the square root of the shot’s weight, which would both augment the force of the blow with which it would strike, and also the extent of the range.
Compound-shot, or shells filled with lead, fired with charges increased ⅛th, will increase the power of range considerably.
11.With common shells at 45° elevation, the time of flightis nearly equal to the square root of the range in feet, divided by 4; or, more nearly, equal to the square root of the quotient of the range in feet, divided by 16-1/12.
12.The range at 45° elevationis nearly equal to the square of the time of flight in seconds, multiplied by 16-1/12 feet. The range at 15° will be about half that at 45°.
13.Upon inclined planes, at any elevation, there are always two elevations with which any range may be obtained.
The elevation which gives the greatest range, on a given ascent, is equal to half the sum of 90° added to the ascent.
The elevations which give equal ranges on a given ascent, are the complements of each other added to the ascent.
The elevation which gives the greatest range on a descent, is equal to half the complement of the descent.
14.The depths penetrated by balls of the same size into wood, with different velocities, or charges, are nearly as the squares of the velocities. Balls of different sizes will penetrate to depths proportionate to their diameters; therefore a greater ball will not only make alarger hole, but will also penetrate farther than a small one with the same velocity.
15. By experiments at a mean range, it has been ascertained that in common earth, dug up and well rammed, a musket ball buries itself nearly 1½ foot; a 6-pounder from 3½ feet to 4½ feet; 9-pounder from 6½ feet to 7 feet; 12-pounder from 8½ feet to 10 feet; 18, and 24-pounders from 11½ feet to 13 feet.
THEORY, AND PRACTICE OF GUNNERY,
APPLICABLE ESPECIALLY TO THE SERVICE OF NAVAL ORDNANCE.[29]
Double Shotting.
“Double shotting may be used with all 32-pounder guns above those of 32 cwt., at distances not exceeding 400 or 500 yards; but the most efficient practice with two shot is at 300 yards. The 32-pounders of 32 cwt. and 25 cwt. should not, however, be so used beyond 200 and 250 yards.
“With double loadings of round shot and grape, when the shot is put in first, the projectiles range more together than when the reverse process is used; such loading requires, however, more elevation to be given to the gun than when single shot are used, on account of the grape shot impeding the flight of the round shot. A double load of grape from the same gun ranges tolerably well together for 300 yards. With a double load of case shot, even with half a degree more elevation than when a single load is used, a great many balls will not range above 100 yards to the first graze; within this extent they lose much of their velocity, and few reach an object at 200 yards. A 32-pounder gun of 56, or of 50 cwt., double shotted with charges of 6 lb., requires at 400 yards 1½ degree of elevation; at 300 yards 1 degree; and at 200 yards half a degree; and, in general, half a degree must be added, with any double loading, to the elevation required with single shot.
“For round, and grape, at 400 yards, there is required 1½ degree of elevation; and at 200 yards half a degree. These projectiles range well together at a target, but they should not be used at a greater distance than 150 yards on account of their dispersion, and the differences of their striking velocities, and penetrating forces.
“With a single load of grape at 400 yards, the elevation required is 1 degree, a full charge of powder being used. With a double load of grape at 400 yards, and the reduced charge, the elevation required is 3½ degrees; at that distance, however, double grape scatters so much as to make very bad practice.”
The effects of wads.
“Experience has proved that different degrees of ramming, or different dimensions of wads, make no sensible alteration in thevelocities of the ball as determined by the vibrations of the suspended gun. Stout firm junk wads, so tight as with difficulty to be rammed into the gun, have been used; sometimes they were placed between the powder and ball, sometimes over both, but no difference was discovered in the velocity of the ball. Different degrees of ramming were also tried without wads. The charge was sometimes set home without being compressed; sometimes rammed with different numbers of strokes, or pushed up with various degrees of force; but the velocity of the ball remained the same. With great windage, the vibrations of the pendulum were much reduced, although tight wads under the shot were used; so that wads do not prevent the escape of the inflamed powder by the windage, nor under any circumstances occasion any sensible difference in the velocity of the ball.[30]
“From experiments made on board the ‘Excellent,’ in 1847, it was found that a grummet wad is more efficient than one of junk, in preventing the cartridge from shifting its place in the bore when the guns were run out with a strong jerk.
“With respect to small arms, it is found that wads of different kinds have different effects upon the projectile, by modifying the action of the charge; and from experiments which have been made in the United States with a musket pendulum, the following results have been obtained: With a charge equal to 77 grains, a musket ball, wrapped in cartridge paper, and the paper crumpled into a wad, the velocity of the ball was 1342 feet; and when two felt wads, cut from a hat, were placed on the powder, with one on the ball, the velocity was 1482 feet. With a charge equal to 140 grains, two felt wads being placed on the powder, and one on the ball, the velocity was 1525 feet; when cartridge paper was used, crumpled into a wad, the velocity was 1575 feet; and when one wad of pasteboard was placed over the powder, with another on the ball, it was 1599 feet. These results seem to indicate that wads made of the stiffest materials are the most advantageous.”
Penetration of Shot.
“Experiments were made in 1848 on board H.M.S. ‘Excellent,’ by firing both solid and hollow shot against the ‘Prince George’ hulk, which was moored at the distance of 1200 yards. The guns were laid at small angles of elevation, generally between two and three degrees; and the following is a brief statement of some ofthe most remarkable effects which were produced, the depth penetrated being expressed by the sum of the distances in solid wood which the shot passed through, or deeply furrowed. Several 18-pr. shot, with charges of 6 lb. of powder, penetrated to depths varying from 21 to 33 inches, according to the state of the wood, and there stuck. With charges of 8 lb., the 32-pr. shot penetrated to depths varying from 22 to 48 inches. A 68-pr. shot (solid), with a charge of 10 lb. of powder, made a total penetration of 46 inches. Many hollow shot were fired with remarkable effects from 68-pr. guns, making penetrations which varied from 25 to 56 inches. One of these, with a charge of 8 lb., penetrated the side of the hulk, passing through 28 inches of good wood, tore out the iron hook, which holds the port-hinge, and fractured the after-side of the port, driving the splinters about the deck. It rent away the end of a beam, grazed the deck, passing through two planks, and cutting down a stanchion 8 inches square, making several large splinters; it then struck against the opposite side of the ship, whence it rebounded against that which it entered.
“At 800 yards, with heavy guns, a charge of one quarter of the weight of shot may always be used; at 500 yards, the charge may be reduced to one-sixth; and within 400 yards, two shot at once may be used with advantage.
“Hollow shot from a 68-pounder carronade, with a charge of 5 lb. 8 oz., penetrated to depths varying from 28 to 31 inches.
“In order to ascertain if shot reflected from water would damage a ship, shots from a 32-pounder gun, with a charge of 10 lb. and a depression equal to 7 degrees, were fired, and the following are some of the effects produced:—
“At the distance of 16 yards, the shot struck the water at 4 feet from the ship’s side; and in one experiment it lodged in the cut-water; in another, it indented the ship’s side; and in both cases it struck at 18 inches below the water-line. At the distance of 36 yards, with a depression of 5 degrees, the shot struck the water at distances from the ship’s side varying from 2 to 15 feet; and, ricocheting, entered the ship at distances above the water-line varying from 2 inches to 3 feet. In consequence of the loss of force which the balls sustained by striking the water, it has been inferred, that if a shot be fired with such a depression as a ship’s gun will bear, it will not penetrate into water more than 2 feet; and, consequently, it will be impossible to injure a ship materially by firing at her under water.
“From experiments made at Metz, in 1834, it appears that masses of cast iron, above one yard square and thirteen inches thick, do not resist the shock of balls fired against them with even moderate velocities, having been fractured not only at the point of contact, but also at points considerably distant from thence. It was found, also, that the side of a traversing gun carriage of iron was broken by an 8-pounder ball, having a velocity of 492 feet; which proves that carriages of this nature would, if struck, be rendered unserviceable:and that a collision, which, with a wooden carriage, would have damaged only an accessory part, without requiring its being replaced, would, with a cast-iron carriage, have a more fatal effect. Not only is the object struck destroyed, but the fragments scattered in different directions are highly dangerous.
“During the year 1850, various experiments were made on board the ‘Excellent,’ at Portsmouth, in order to ascertain the effects which might be produced on iron vessels by shot, both solid and hollow, with various charges of powder; for which purpose a double target, ⅝ of an inch thick, consisting of iron ribs and plates, resembling the opposite sides of a strongly-built iron steamer, was constructed, at the distance of about 450 yards from the ship. The general effect was, that the target was always pierced by the shot, and that numerous splinters were detached from it in every direction, which could not fail to be most destructive to the crew of a vessel of this description; the shot was, besides, almost always split in pieces by the shock. One 32-pounder shot broke into thirty-four fragments. Some experiments were made with grape-shot, fired from a 32-pounder, with charges of 3 lb. and 6 lb., when the shot passed through a plate, making a clean hole 3 inches in diameter, and knocking out some rivets. The effects produced by 6-inch shells were not greater than those produced by shot. Two of these being filled with powder, and having the fuze holes plugged up, broke on passing through the plate; the powder, however, did not explode, but was seen to go away in a cloud like dust.
“From the above-mentioned experiments, it may be concluded, that the splinters detached from the side of an iron ship, and the fragments of the shot themselves, would as effectually clear her quarters as the explosions of shells; in either case the effect would be more serious than any that could be produced by like means on a ship constructed of timber, incendiary effects excepted. With both raking, and diagonal firing, the effect is described as being most formidable; the holes, which were very irregular, were in all cases larger than the shot.
“In 1838, experiments were made at Gavre with two solid balls fired at once against a butt of oak timber, in order to determine the different penetrations of the shot, and the distances between their centres at different distances from the piece. Three different natures of ordnance were used: a long 30-pounder gun, a cannon obusier of 30, and a 30-pounder carronade. One ball was in contact with the charge, and the other in contact with the former. From these experiments it was evident that the ball which was in contact with the charge had the least velocity, and the least penetrating power. It is further remarkable that, at distances beyond 200 yards, the vertical dispersion greatly exceeds the horizontal dispersion.”
Excentric spherical shot.
“Experiments with these projectiles were carried on at Metz in 1841; the following were the effects observed:—When the centreof gravity was above the centre of the figure, the ranges were the longest, and when below, the shortest; when to the right, or left hand, the deviations were also to the right, or left. The mean range of a 12-pounder brass gun, which, with the usual shot, was 1640 yards, was, with the shot whose centres of gravity and of figure were not coincident, the centre of gravity being upwards, equal to 2140 yards, being an increase of 500 yards.
“When the centre of gravity is not coincident with that of figure, the projectile is made to revolve,ab initio, on the former centre, thus occasioning a compound motion in the flight of the projectile. When the centre of gravity is below the axis of the bore, the front must turn from below upwards, and a rotation in this direction continuing, the range will be diminished. In like manner, when the centre of gravity is placed on the right, or left hand of the axis of the bore, the shot will turn on a vertical axis, and produce deviations to the right, or left hand respectively. Experiments were carried on at Portsmouth, and at Shoebury Ness, in the year 1850, to ascertain whether the deviations of excentric projectiles were so regular as to admit of being allowed for in pointing the gun; and whether any result might appear to disprove the maxim, that spherical and homogeneous projectiles are the truest in their flight.
“The preceding table presents, in an abstracted form, the results of the experiments at Portsmouth, and Shoebury Ness. It will be observed that the ordnance used were 32-pounders, and 8-inch guns; from both of which natures were fired the ordinary solid shot, and also shot rendered excentric by the removal of certain quantities of metal. Thus, in the Portsmouth experiments, 1 lb. of metal was taken from each 32 lb. shot, and 3 lb. from each 68 lb. shot; in those at Shoebury Ness, 1 lb. or 2 lb. were taken from the 32 lb. shot, and 4 lb. from the 68 lb. shot.
“On analyzing the experiments, both at Portsmouth, and Shoebury Ness, it appears that the flight of the ordinary solid shot was the most true, the lateral deflections being frequently but one-half, sometimes one-third, or one-fourth only of the deflections of the excentric shot; that these last deflections were always in the direction in which the centres of gravity of the shot were placed in the gun; and that the increases, or diminutions of range caused by the vertical deviations were produced respectively, as the centres of gravity of the shot were placed upwards, or downwards. It appears, also, that the lateral deviations, though in general constant in direction, were very variable in amount. The results above stated prove decisively the correctness of the deductions from theory, and of the practical maxim, that errors in sphericity and homogeneity in a shot are causes of its deviation from a correct path; and it follows that spherical and homogeneous projectiles, being the most simple, and quite indifferent to the position in which they are placed in the gun and rolled home, as well as to that in which they pass through the atmosphere, are decidedly to be preferred to the others.
“The results of these very curious, and instructive experiments fully explain the extraordinary anomalies, as they have hitherto been considered, in length of range, and in the lateral deviations: these have been attributed to changes in the state of the air, or the direction of the wind, to differences in the strength of the gunpowder, and to inequalities in the degrees of windage. All these causes are, no doubt, productive of errors in practice; but it is now clear that those errors are chiefly occasioned by the excentricity, and non-homogeneity of the shot, and the accidental positions of the centre of gravity of the projectile with respect to the axis of the bore.
“The whole of these experiments furnish decisive proof of the necessity of paying the most scrupulous attention to the figure, and homogeneity of solid shot, and the concentricity of shells; and they exhibit the remarkable fact, that a very considerable increase of range may be obtained without an increase in the charge, or elevation of the gun.”
Resistance of iron plates, oak plank, &c., against musketry, canister, grape shot, hollow, and solid shot.
“From experiments in November, 1849, the following results were obtained:—
“Marine percussion musket—Charge, 4½ drams; distance, 40 yards.
“Experiments were made in June, 1850, against two sections of the ‘Simoom,’ ⅝ inch thick, placed 35 feet apart; the guns, and charges were those used in all steam vessels. The result made evident that two, or three shot, or sometimes even a single one, striking near the water-line of an iron vessel, must endanger the ship. Another most serious evil is, that the shot breaks, on striking, into innumerable pieces, which pass into the ship with such force, as to range afterwards to a distance of 400 or 500 yards; and that the effect on men at their quarters would be more destructive than canister shot, supposing them to pass through a ship’s side; as when the plates are only ⅜ inch thick.
“Experiments were made in July, 1850, against an iron section similar to the ‘Simoom;’ it was filled in and made solid with 5½ inch oak timber between the iron ribs, and 4½ inch oak planking above the water-ways, which were 1 foot thick, and with 3 inch fir above the portsills; these were strongly secured to the iron plates by bolts. The results were as follows:—The holes made by the shot were not so irregular as on the former occasion, but as clear and open; all parts of the shot passed right through the iron and timber, and then split, and spread abroad with considerable velocity. With low charges, the shot did not split into so many pieces as before. With high charges, the splinters from the shot were as numerous and as severe as before, with the addition, in this, and the former case, of the evil to which other vessels are subject—that of the splinters torn from the timbers.
“In August, 1850, an iron section similar to the ‘Simoom’ wasprepared with a covering of fir plank on the outside, of the thickness of 2, 3, and 4 inches, in different parts. The result of this experiment was similar to the last, when the wood was on the inside; with the exception of the splinters from the wood. The holes made by the shot were regular, of the full size of the shot, and open; every shot split on passing through—those between the ribs into a few pieces only, those that struck on the ribs into a great number; in both cases, when combined with the splinters of the iron side, the effect must prove highly destructive.
“A comparison as to the effect of shot on iron, and timber, was made by firing 8-inch hollow shot, and 32-pound solid shot, at a butt built for experimental shell-firing, with timber having 6-inch plank on the outside, and 4-inch within; the result was, that the splinters from the wood were trifling when compared with those from the iron.
“The general result of all the foregoing, and consecutive experiments for the same purpose, clearly demonstrates that the destructive effects of the impacts of shot on iron cannot be prevented. If the iron sides are of the thickness required to give adequate strength to the ship (⅝, or at least 4/8 of an inch), the shot will be broken by the impact; if the iron plates be thin enough to let the shot pass into the ship without breaking, the vessel will be deficient in strength; the shot will do its work, particularly in oblique or raking fire, more effectively than its splinters, and, in passing out, make apertures more difficult to plug or stop, than in passing in. When a clean hole is made by a shot penetrating an iron plate, the whole of the disc struck out by the shot is broken into numerous small pieces, which are driven into the ship with very destructive effects; and if the plate be so thick (viz., upwards of 4/8 of an inch) as to cause the shot to break on striking, the fragments will nevertheless pass into the ship, as in the case of a percussion, or concussion shell, and so produce a terrific compound effect by the fragments of both.
“The expedient of combining wood, and iron, either by substituting timber for the iron ribs, or the reverse, outside planking for the iron plates—makes the matter worse. The pieces of ribs struck off, sometimes of great length, pass on with the shot, to produce more extensive ravages elsewhere.”
“In firing into masses of timber, or any solid substance,that velocity which can but just penetratewill occasion the greatest shake, and tear off the greatest number of and largest splinters; consequently, in close actions, shot discharged with the full quantity of powder tear off fewer splinters than balls fired from the same nature of guns with reduced charges.
“In naval actions, shot intended to take effect upon the hull of an enemy should rather be discharged with a falling than with a rising side; but such pieces as may be appointed specially to act againstthe masts and rigging should be fired, on the contrary, with the rising motion, the aim being taken low.
“In all close actions, the great object should be to strike as often as possible the enemy’s hull. One or two 24-lb. shot taking effect just below the water-line, and perhaps perforating both sides of a small vessel, will in general either force her to surrender, or send her to the bottom; and such an injury is much more likely to be occasioned by firing with a falling than with a rising side.
“To estimate the distance between vessels.[31]
“Measure with a sextant, or quadrant, the angular height of the enemy’s mast, and by referringto Table B, the corresponding distance may be taken out.
“In Table A, the height of the masts to the head of the maintopgallant rigging, and likewise to the maintopmast crosstrees above the surface of the water at low water mark, are given for every rate, and class of vessel.
“The distances in English yards, corresponding to the angles subtended by the masts, are given in the first columnof Table B.
“Table Bmay also be applied to the important purpose of determining distances, making use of the ship’s own mast as the given height or side of the triangle, by marking upon it any of the heights expressed in the table, and placing an observer there when required to measure the angle A B C (vide fig.) formed by the mast when most perpendicular, and the line of sight B C.
Right triangle ABC
“The Tangent practice TablesC, D, and E will frequently be found useful in pointing ordnance, when the distance is known; for by referring to that distance in the column of the table belonging to the corresponding nature of gun, the part, that should be aimed at, will be ascertained.”