At very short distances from the muzzle of the gun the penetration was found to be less than at distances more extended. At five yards the iron plate could not be perforated; at ten yards the effect was much greater, but fifteen yards was the least distance at which it could be said to be effectually perforated; at twenty yards the result was still more satisfactory, clearly demonstrating that bullets gain both in velocity and penetration for a considerable distance after leaving the muzzle of the gun. The following experiments verify this remark:—
In the report of the experiments which were carried on at Cork in 1852, it is stated that the power of penetration of an elongated rifle bullet gradually increases as the range is increased, up to 190 yards.
In order to prove this, experiments were carried on at Enfield for three days with a variety of fire-arms, and different sorts of projectiles. On the fourth day the experiments were repeated with the common musket and Wilkinson’s rifle. The former, at forty yards, gave a penetration of 2·25 inches; and the latter averaged 2·75, in a target of green elm. Again: at ninety yards, the musket penetrated 2·25 inches, and the rifle 3·5 inches. At 120 yards, the musket gave 2·5 inches, and the rifle 3·25. Both being subsequently fired at every successive ten yards up to 220, the result was that the penetration of the musket ball gradually decreased in power as the distance increased, while the elongated bullet gained power of penetration up to 190 yards; after which it slightly decreased.
2nd. Consequent on the velocity of the explosive fluids is the resistance of that aëriform fluid filling all space. It has been calculated that in a vacuum, matter in motion would be a long time in coming to rest; and very providentially it is that nature in her grand arrangements has made one element to control another. In no other portion of nature’s work has anything more wonderful than atmospheric air been produced; its action on the velocity of projectiles is of so extensive a nature, that without clearly understanding that action, the science of gunnery never can be thoroughly acquired. The resistance of the atmosphere is in proportion to the velocity of the attempt to displace it; the higher that velocity becomes, the greater is the resistance. This is shown by the actions of all the fulminates. A quantity of the fulminate of silver exploded on a copper plate will perforate that plate, or, if fired upon a piece of wood, will bury itself in that substance, splintering it in proportion to the quantity. Now, ordinary gunpowder has no such effect as this, because, though it may produce the same amount of expansive gas, it produces it at one-fourth the velocity of the fulminates: the air is driven back upon itself so gradually as to offer no very important resistance; but the action of the fulminates is so rapid and so violent that the high elasticity of the air has not time to yield, and the force is driven into the apparently more solid material, the copper or the wood.
The mode in which atmospheric resistance mostly interferes with projectile force is owing to the columnar form it assumes in the tubes of all descriptions of gunnery. If the velocity of gunpowder be as great as we suppose it to be, the displacement of a column of air must be effected by driving the whole column in a gun-barrel of many inches, into a column probably less than half an inch in height; or, if the length of the tube from the starting of the charge to the muzzle be 38 inches, then will the displacement require a force capable of condensing thirty-eight atmospheres into one, or something like 570 lbs.; without estimating the lateral pressure of that column on the sides of the gun-barrel, which may be safely estimated at one-half more. It may be supposed that the column would be partially in motion for a greater distance than half an inch in front of the projectile; but this is disproved by the fact that time is essential to put aëriform matter in motion, and naturally it never does so at a greater velocity than it is familiarly known to do in the shape of winds: but the fact is better illustrated by the frequent bursting of barrels near the muzzle, caused by a piece of snow or clay, a piece of paper or wadding. Were a current established around this projection it would pass on, but the air strikes these light obstructions when in a high state of condensation, amounting to many atmospheres in one: so many as to be nearly equal to a solid which is more powerful than the barrel; the latter therefore succumbs to it.
The resistance of the air is so highly philosophical a question, that I merely touch on its actual bearings on the passage of projectiles to show how the quantity of force is absorbed or expended in relation to the quantity of the gunpowder employed; which, it may be assumed, is a proportion of nearly one-third of the whole, or a quantity independent of that necessary to give velocity to the leaden projectile, to enable it to overcome the still and uniform impeding agent up to the end of its flight. The rapid exit of the bullet from the barrel, with a resisting influence of this weight into the comparatively insignificant one of 15 lbs. to the square inch, will fully explain how it is that a bullet increases in velocity even up to a considerable distance after leaving the muzzle of the gun; and further showing that in all arrangements of truly scientific gunnery, the increasing resistance must be met by a fresh production of explosive fluid over every atom of space in that tube, where it is demonstrable that the resistance is increasing in a geometrical progression as the point of exit is becoming nearer; so that gunnery, unless all the contingencies are provided for, must necessarily remain an imperfect science.
Intimately allied to the displacement of the atmosphere is the amount of friction. Gunnery is now rid of the anomaly of being assisted by friction: the detention of the projectile in the tube by artificial friction, to enable more force to be generated, is one of those absurdities pardonable only in bygone days. Science is best consulted by lessening friction; guns of steel, with interiors as fine as the polish in a mirror, are found to shoot best: a rough road is but so much force uselessly absorbed; the experience of the last few years having proved that a range of 1,800 yards cannot be accomplished except with barrels having surfaces as smooth as possible.
Rifles, no doubt, are now in use in which, by increasing the degree of spiral, friction is more than doubled, perhaps trebled; but such unscientific constructions are but as one error to counteract another. Unscientifically formed projectiles not having in themselves the principles necessary for true flight, have to receive a counteracting agency in the shape of additional spinning, on an axis coincident to the line of flight, to enable them to range a given distance, with, as it will be perceived, an additional amount of expellant agency; but these cannot be included in the category of scientific gunnery.
3rd. Next to absence of friction is the construction of the gun barrel. Already have we shown that the inner surface of a gun barrel requires to be like glass; next to this it is necessary that the metal should be composed of the most unyielding structure. Metals absorb force in proportion to their softness: a barrel constructed of lead gives the worst result of any metal; in truth, as is the increase of tenacity and density in the tube, so is the increase of range in projectiles. The wonderful results displayed by the use of steel guns of all descriptions bear out this assertion to the fullest extent. A yielding gun barrel may be compared to the dragging of a heavily loaded waggon over boggy ground, which rises in a wave before the wheels during its progress.
4th. Next in importance to the inflexibility of the gun barrel is the form of projectile best calculated to displace the atmosphere during its extended flight. Under the head of [Rifles] this subject will be more fully discussed; but, as thousands of years have stamped the arrow as being in accordance with nature’s laws, it should no doubt be the object of science to approximate the leaden projectile to that form as much as possible, and hence the cylindro-conoidal may be assumed to be the best form of projectile.