Recoil.
Recoil varies according to the position of the gun; when fired on the horizontal, the resistance to be overcome is the tendency of the projectile to fall to the earth, and its friction as it moves in a line parallel to the earth. When the muzzle is elevated this resistance is increased, because the force generated by the explosion of the gunpowder has to exert its action more directly in opposition to the direction of the force of gravity; and when this force is exerted in a line directly opposed to the centre of gravity, as it is when the gun is fired vertically, then the recoil is doubled, and is made more painful, because the body resting on the earth cannot yield.
A gun fired in the direction of the earth, or in the line of the centre of gravity, would recoil much less (perhaps fifty per cent. less) than when fired vertically; from the very obvious fact, that if the bullet was not kept in position by its friction on the sides of the barrel, it would fall to the ground of itself.
“The recoil of a gun is inseparable from a discharge of its contents—on the broad principle that action begets reaction; it is, therefore, only when the ‘kick,’ as it is called, becomes painful, that it is essential to avoid or lessen it. Irregularity in the bore of the barrel is a very common source of violent recoil; contracted breeches also, but more than all, the contraction of the barrel at its centre, occasion recoil, and that of the most dangerous kind: the expanding flame, during its ignition, presses violently to make its way through the contracted to the wider part, thus also destroying the expelling force. ‘Now, action and reaction being equal, it follows, that the weight of the piece being the same, the recoil will be in proportion to the quantity of the powder, and the weight of the ball, or shot; and that with the same charge the recoil will be in proportion to the weight of the piece, or the lighter the piece the greater the recoil.’”—Essay on Shooting.
Here is a true exposition of recoil, though not of contractions in the breech; for there the action would not be directly back, but have an inclination towards the muzzle; for the reaction would not have time to tell on the breech, before the charge was out of the muzzle. An extremely spiralled rifle barrel destroys the explosive force of gunpowder, but the effects are not felt in the recoil, being most all expended laterally. Blaine says, “Could we entirely obviate all recoil from a gun, we should not only remove an unpleasant shock to our persons, but there is reason to believe we should much assist the range and force of the shot likewise; although there is an opinion prevalent, that the degree of the recoil is in the proportion of the projectile force.” Of this, however, some doubts are entertained, which are warranted by the following fact:—“Mortars with iron beds immoveably fixed in the earth throw their shot to greater distances than guns which are affixed to carriages can do, and which, therefore, can recoil. This has been incontestibly proved, both in large and small artillery. Having suspended a gun barrel, charged with a determinate quantity of shot, from the ceiling by two cords, so as to allow of its recoil, fire it point blank at a target, and mark the result accurately. Now, fix the same barrel to a block, and charge it exactly with a similar charge; then having moved the target fifteen yards further, fire the barrel; it is probable that the last shot, though at this increased distance, will exceed the former, both in range and force.’ These and such like experiments are laughed at by the giddy and inconsiderate; but it is by these illustrations that the most important facts are brought to light.
“Projectile force is, therefore, to be increased by resistance; and the knowledge of this fact offers us a practical hint, that when we stand immoveable to our shot, not only by holding the gun tightly to our shoulder, but by also leaning somewhat forward in our shooting attitude, we considerably increase the resistance, and, consequently, we not only lessen the shock of the recoil to ourselves, but we aid the force of the shot and extend its range. That such is the case, may be further exemplified by the following experiment:—Throw a hand-ball against any moveable body, and it will displace that body; but the ball will drop to the ground perpendicularly, however hard the body against which it is thrown may be. Fix the same body securely, and then the rebound of the ball will be nearly equal to the force with which it was thrown.”
The weight or amount of force with which a gun recoils against the shoulder, is due to, and regulated by, several circumstances. The first and most important is the amount of explosive force generated before the charge is moved and during the act of moving, and the amount of inertia in the body of the projectile. When a quantity of gunpowder is exploded without any resisting weight in front of it, then the column of air gives comparatively a slight recoil; though there is, in fact, considerable recoil, but such as is due to the resistance of the air only, and, consequently, more like a push than a blow. The exact amount of recoil is also due to the difference between, or proportionate weights of, the charge of shot or bullet and the gun; action and reaction being always equal until one or the other body moves; the division then will be in favour of that moving fastest, and hence the obtaining of accelerative velocity: it thus follows, as a truism, that the smaller the quantity of exploded gases that can be employed to first move the charge, the less the recoil.
The advantage of the granulation system is here again most clearly shown; and (alluding again to the law of putting matter in motion gradually) if you would gain the greatest benefit, it is clear that, in the same length of tube, you would, at the termination of the accelerative power, have gained a much greater amount of velocity than could be obtained under any other circumstances with the more violently explosive gunpowder.