BULLETS OF VARIOUS SHAPES

305

to penetrate the water, and not to glance off it, like ordinary pointed shot. The best theoretical shape for penetrating air with the least resistance has a sloping stern to it as well as a bow, but the attempts of Sir Joseph Whitworth to make use of this form in projectiles for big guns have not been followed up, and the shape introduces certain practical difficulties. Fig. 73 shows the Whitworth shot with tapered rear, and fig. 74 a tubular bullet of which he thought highly, finding it to give great penetration and to cut a core out of elastic substances. In 1893, some sensation was caused by

FIG. 73

FIG. 74

FIG. 75

the production of the Krnka-Hebler tubular bullet, which had long curved lines towards bow and stern, and which was solemnly announced to maintain its velocity and penetration in a wonderful degree up to extreme ranges; unfortunately it was not found to stand the test of actual experiment in these respects.

The difference in shape introduced by Mr. Metford will be seen if the 303 bullets on p. 142 are compared with that of the Martini-Henry on p. 71. Any economy in air-resistance is effective more and more as the range increases.

The bullets of the 303 rifle do not ricochet off turf at

X

3,000 yards, and very few of them beyond 2,000 yards. At distances approaching the extreme range of the rifle, the impulse of projection is largely exhausted, and the velocity with which the bullet strikes is due in part to its speed of fall under the influence of gravity. But it has little penetration. The direction of ricochets from a smooth surface such as calm water, naturally follows that of the spin, but on ordinary ground it is very uncertain.

CHAPTER XII

MOVEMENT OF THE RIFLE IN FIRING-ITS VIBRATIONS-EARLY IDEAS AS TO PATH OF PROJECTILE THE TERM POINT BLANK'-JUMP AND FLIP— EFFECT OF BOLT FASTENING ON DIRECTION OF FIRE-AND OF AFFIXING BAYONET-EFFECT OF VIBRATIONS ON ACCURACY-COMPENSATORY ACTION -FRICTION IN THE BORE-FIRST SHOT FROM CLEAN BARREL-SHAPE OF BULLET-HOLE-SPIN OF BULLET-ITS STABILITY RATE OF SPINPICTURES OF BULLETS IN FLIGHT-AIR WAVES-BULLETS VISIBLE IN OF EARTH'S ROTATION-GROUPING OF

FLIGHT-DRIFT-INFLUENCE

SHOTS THE BALLISTIC PENDULUM-THE ELECTRIC CHRONOGRAPH

IN the skirmishing kind of fire so often necessary on service, which approximates to fire under sporting conditions, and which is likely to be much more the rule in future than hitherto, the positions depend very much on the form of the ground, and on the circumstances of the moment. It is of practical importance always to rest the rifle, if this can conveniently be done. The Volunteers in Plate XLII, which has been taken from a little book published by Ackermann forty years ago, illustrate this point, though the trees from behind which they are firing would not in these days afford complete protection. The marksman whom Ezekiel Baker depicts shooting in the prone position. (Plate XXX) has taken off his tall plumed hat (no doubt so made that the crown is of a convenient height for this purpose), and, having placed it on the ground in front of him, rests his rifle upon it. Such assistance in steadying the aim requires to be used with discretion. It is as well not to rest the rifle nearer the muzzle than can be helped. The normal movement of the rifle under the influence of the recoil, which begins before the bullet leaves it, and which is taken into account in sighting it when fired in the ordinary way, is apt to be disturbed by any support or restraint, and it may be that a slightly abnormal flight of the shot will be the consequence, which will lead to failure if great accuracy is essential. The ordinary military rifle does not seem to be easily disturbed in this respect, if rested near the

middle of the fore end. It is a matter of common knowledge that in a double rifle or gun, the two barrels have to be set so as to converge somewhat towards the muzzle, and that if they are carefully examined the axes of their bores will be found, if prolonged, to cross at a little distance in front of the muzzle. The outward movement of the recoil, which swings the muzzle to the right when the right barrel is fired, and vice versa, compensates for this convergence, and the barrels, if properly adjusted for a given charge, will shoot parallel to each other. The sighting of a rifle is similarly disturbed by any appreciable variation from the normal charge. It may even be that by reducing the charge it will at a short range be found to shoot higher, and by increasing it to shoot lower. It is important, then, that the sighting of a rifle should be checked if there is any variation of the charge, either in the weight or composition of the bullet, or in the amount or nature of the explosive. If the barrel were free to recoil precisely in the direction of its own axis, and if the centre of gravity of its mass, with the fittings attached to it, were in the axis of the barrel, or in the prolongation of it, we may suppose that it would shoot quite normally, and that its sights would be correct, if their base line, or zero line, were made parallel to the axis of the bore; but it may be said that the correct line of sighting never fulfils these conditions. It is well known that in a pistol, or revolver, the fore sight is a good deal higher above the barrel than the back sight, to compensate for the upward kick which takes place before the bullet leaves the muzzle. With the longer barrelled rifles the vibrations are more complex, and the line of the zero may diverge either above or below the line of the axis of the barrel when at rest. In the Lee-Metford there is normally an upward throw of about 20 to 25', hence the necessity for a high fore sight.

It is evident that a long barrel when under the influence of the explosion of the powder is thrown into a state of vibration, the length of the waves of vibration depending upon the proportions of the barrel. This is truly the case with an unsupported barrel, but the vibrations seem to be checked and modified when the barrel is attached to a stiff and heavy fore end. If the barrel be supported at one of the nodes of vibration its free movement will not be interfered with, and,