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THE SPORTING RIFLE.
THE THEORY OF RIFLE SHOOTING, AND THE MODE
OF RIFLING THE BARREL.
DEFINITION OF THE RIFLE-VELOCITY DIMINISHED BY RIFLING A SMOOTH
BORE-GREATEST AT THE MOMENT WHEN THE BALL LEAVES THE MUZZLE-VARIETIES IN THE FORM OF THE GROOVES ALMOST INFINITE-THE BARREL-METHOD OF RIFLING-TECHNICAL TERMS.
A rifle may be defined to be a species of gun which causes its projectile to rotate around the line of its flight. This is effected by means of spiral grooves or channels, which are cut on its internal surface, sometimes so slightly as to be invisible to the eye, but generally with a sharp margin. The consequence of this form is, as described by Robins, “that when the piece is fired, the indented zone of the bullet follows the sweep of the rifles; and thereby, besides its progressive motion, acquires a circular motion round the axis of the piece, which circular motion will be continued to the bullet after its separation from the piece; by which means a bullet discharged from a rifled barrel is constantly made to whirl round an axis which is coincident with the line of its flight. And hence it follows, that the resistance of the foremost end of the bullet is equally distributed round the pole of its circular motion, and acts with an equal effect on every side of the line of direction, so that this resistance can produce no deviation from that line. And (which is still of more importance) if, by the casual irregularity of the foremost surface of the bullet, or by any other accident, the resistance should be stronger on one side of the pole of circular motion than on the other; yet, as the place where this greater resistance acts must perpetually shift its position round the line in which the bullet flies, the deflection which this inequality would occasion, if it acted constantly with the same given tendency, is now continually rectified by the various and contrary tendencies of that disturbing force during the course of one revolution.”—Tracts, p. 330.
VELOCITY DIMINISHED BY RIFLING A SMOOTH BORE. Such is now the admitted object of the grooves in the rifle; and it is unnecessary to support the view taken by Robins and others since his time, by the analogy of the top or the arrow. Whether the latter rotates or not in its flight is perfectly immaterial, for if it does, the motion is communicated by the air through which it passes, and not by the bow or the hand before it quits them. A ball from a smooth bore (that is, from a barrel not rifled in any way) will have a greater velocity and range than a similar ball projected from a ritled barrel, on account of the friction caused by the rifling absorbing some portion of the original force of the explosion. Hence, neither increased range, nor its synonym, velocity, is gained by ritling, but only truth or correctness of flight; so that, though the ball does not really go further, it will be of service at a greater range, because it will hit the object at which it is aimed. At the same time, the introduction of rifling may be said to increase our range—not, it is true, in the use of spherical balls, the flight of which it retards— but because from the spinning motion given to it, a more elongated ball may be used than from a smooth bore; and hence the weight being increased in a greater proportion than the area to which the atmosphere offers resistance in its passage, the flight is greatly extended. In a smooth bore a slightly oval ball can be relied on, if one end is somewhat thicker than the other (or egg-shaped), for that end being heavier will always fly forward; but a pointed cylinder soon “upsets,” as it is termed, and is then at once rendered useless as a projectile. By upsetting is to be understood the turning
sideways of an elongated ball, and it is this accident which forms the chief impediment to rifle shooting. The impetus being given to the hind end of the ball, while the resistance of the air is offered on the front, there is a constant tendency to the one overtaking the other, in doing which the ball must necessarily offer its side to the point at which it is aimed. The greater the spin the more this tendency is checked, for no sooner does the base begin to turn over to the right, than it is forced round to the left, and so on in succession to every point in the circle of which its line of flight is the centre.
VELOCITY GREATEST AT THE MOMENT OF LEAVING
It has been found by experiment that a ball will pierce certain substances at 100 or 200 yards, which it would fail to do at half or a quarter the distance; and upon this fact a theory has been propounded which is adverse to a fundamental law of nature. This theory is, that when the resistance offered by the friction against the sides of the barrel is taken away, the impetus given by the explosion is allowed its full scope, and the ball increases in velocity up to a given point. In fact, it is said that the ball vires acquirit eundo; but Mr. Boucher, in a letter to The Field, completely disposes of this fallacious theory by the following experiment, which I insert as detailed by him.
" Again: with regard to the penetration of shot being, at all ranges, a test of its velocity, the correct interpretation of the law of action and reaction seems, in this case also, to be sadly overlooked and disregarded. I send you six bullets, taken from hundreds of a similar description. See fig. 65. Those marked a and d were fired at 40 yards' distance, and penetrated about one foot; b and e were tired at 100 yards, and penetrated about two feet; while c and f were fired at 200 yards, and penetrated nearly three feet and a half. Now, sir, I have been coolly told in the columns of your paper (March 20) that I am neither a profound thinker nor a careful experimentalist, or I must know the incontrovertible fact that à bullet does gain in speed after leaving the muzzle of the
piece,' and that this fact accounts for the greater force at the longer ranges, ' up even to a range of 250 yards, as some have
surmised.' Yes, I have been coolly told that an absurdity, which is contrary to all the laws of motion, is an incontrovertible fact, because, forsooth, some have surmised it. But, sir, I appeal to you if such a monstrous theory can possibly be true. Look at a and d, which penetrated the shortest distance; they are flattened out, and turned over almost like a mushroom. Is there any indication of want of velocity in them ? No: on the contrary, the velocity or action must have been immense, and the reaction of the sand sudden and equal, or the bullet could not have possibly been so wonderfully altered during the short time which it took to penetrate only one foot. Look at b and e, they show that they were actuated by less velocity, and, consequently, were less altered in shape by the reaction, and therefore penetrated somewhat further. But look, again, at c and fi they penetrated to the greatest depth, but where are the signs of great velocity in them? Their appearance is nearly as perfeet as when they left the muzzle of the piece, and, having less velocity, they met with less resistance or reaction, and consequently, their original elongated shape being less altered, they penetrated furthest of all.
“We have here a beautiful and very instructive illustration of the law of action and reaction, as also of the doctrine of inertia, which deserves a passing comment. Bodies in motion continue in motion from the inertia of motion; bodies at rest continue at rest from the inertia of rest; that is, bodies which move do move, bodies at rest are at rest. This is all. The idea receives colouring from two very important facts. First, the progressive motion of a mass is in proportion to the force impressed, and takes place after a lapse of time from the application of the force to the atoms of the body. There is needed time for the force to be diffused among the atoms by atomic motion, before consentaneous or progressive motion is induced. The other fact is, that in most cases force in moving bodies is gradually applied. Thus a ball fired horizontally over water, with a very sinall charge, will enter the water when it first touches it; for it can, as it were, await the tardy resolution of the atoms of the water into progressive motion to give it place. But when the ball is fired with a full charge, it is deflected, or ricochets. Its velocity is so great that it cannot transfer its force; for it would take many instants for the particles of water, moving with the same velocity with the bullet, to travel through their atomic
space, and to induce progressive motion of the column necessary to be moved for the passage of the ball through the water.
“So it is with sand, wood, iron, &c., for the destruction of velocity is in all cases gradual, and the time employed will depend most materially on the nature of the substance on which the bullet impiuges. The force which the ignited gunpowder generates after having put a bullet in motion and produced its full effect remains, as it were, inclosed in the bullet; and the joint product of the velocity and of the quantity of matter in the bullet represents the result. This joint product is termed the momentum of the bullet. In order, therefore, that the shot should produce the greatest effect, we must move the muzzle of the piece near to the object aimed at; and the nearer we move it the greater the