The How and Why of
Long Shots and Straight Shots

Cornhill Magazine, April 1860

We have before mentioned that Robins pointed out the enormous effect of the resistance of the atmosphere to the passage of a shot; and "because," as he says, "I am fully satisfied that the resistance of the air is almost the only source of the numerous difficulties which have hitherto embarrassed that science," viz. gunnery, he considered it above all things necessary to determine its amount; for which purpose he invented the Ballistic Pendulum and Whirling Machine. His experiments were made principally with small bullets; but a more extended series of experiments was made by Dr. Hutton with the same machines, and on the Continent and in America by Major Mordecai, with a ballistic pendulum of improved construction. It appears from these that when a ball of two inches diameter is moving with a great velocity, it meets with a resistance of which the following examples will give an idea: at a velocity of 1,800 feet per second the resistance is 85 1/2 lbs., and at a velocity of 2,000 feet, 102 lbs. If we wish to increase the range, then, we must overcome this resistance in some way. As the resistance is nearly proportionate to the surface, that is, twice as great on a surface of two square inches as on a surface of one square inch, we must do so by increasing the weight of the shot. For it is evident that if two shot of different weights start with the same velocity, and meet with the same resistance, the heavier one, having the greater momentum, will maintain its velocity the longest. Throw a cork and a stone of the same size with the same force - the cork will only go a few yards, while the stone will go perhaps ten times as far. In the smooth-bored cannon this could only be effected partially by increasing the size of the shot, when the surface exposed to the resistance of the air increased only as the square of the diameter, while the weight increased in a greater ratio, as the cube of the diameter. Hence the longer range and greater penetration of heavy guns. As, how-ever, with a rotating body the tendency is always for the axis of rotation to remain parallel to its original direction - thus a top while spinning may move about the floor, but remains upright on its point, and does not fall till the spin is exhausted - we have with rifles a means by which we can keep a bullet always in the same direction. In order to comply with the condition, then, of exposing a small surface to the resistance of the air while the bullet's weight is increased, we reject the spherical form, and make it a long cylinder; and to make it the more easily cut through the air, we terminate it with a conical point.

Thus compare Mr. Whitworth's 3-pounder with the ordinary or old 3-pounder; the shot weigh the same but the diameter of Mr. Whitworth's 3-pounder shot is 1.5 or 1 1/2 inches, while the diameter of the old 3-pounder shot is 2.91 inches, or nearly three inches; and the surfaces they expose to the resistance of the air are 2.25, or 2 1/4 square inches, and 8.47 nearly, or nearly 8 1/2 square inches; that is, Mr. Whitworth's bullet, with the same weight to overcome it, meets with a resistance of a little more than a quarter that which the old bullet met with, and has the advantage of a sharp point to boot. Hence the enormous range attained, - 9,688 yards.

The very same causes which make the fire of a rifle accurate, tend also to make it inaccurate, paradoxical as it may seem; but this in-accuracy being to a certain extent regular and known beforehand, not of so much consequence, though it is a decided disadvantage. It may - not to be too mathematical - be explained thus: - The axis of rotation having, as we said, a tendency always, to remain parallel to its original direction, when a rifle bullet or picket (the long projectile we have described) is fired at a high angle of elevation - that is, slanting upwards into the air, in order that before it falls it may reach a distant object, - it is evident from the diagram, that if the

direction of the axis of rotation remains, as shown by the lines p p p , which represent the shot at different portions of the range parallel to the original direction in the gun the bullet or picket will not always remain with its point only presented in the direction in which it is moving, but one side of the bullet will be partially opposed to the resistance of the air. The air on that side (in front) will be denser than behind, and the disturbing or deflecting influences before described will come into operation, the two opposite tendencies described in the text and the note to a certain extent counteracting one another. While at the same time the resistance of the air has a tendency to turn the bullet from the sideways position in which it is moving with respect to the line of flight (and the effect of this is the greater the less spin the bullet has to constrain it to keep its original direction), the result of which force, conspiring with the force described in the note, is to give it a slight angular rotation round another axis, and deflect the bullet by constantly changing its general direction (this second axis of rotation) to the side to which the rifling turns. This was exemplified in the late practice with Mr. Whitworth's gun. When firing at the very long range of 9,000 yards the 3-pounder threw constantly to the right from 32 to 89 yards.

The rotation of the earth about its axis tends to throw the projectile always to the right of the object aimed at. Space will not permit of our entering on this subject; but the principle is the same as that which in M. Faucoult's experiment with the vibrating pendulum caused its plane of vibration apparently to constantly deviate to the right.

The time of flight of the shot from Mr. Whitworth's 8-pounder gun is unknown to us; we are unable, therefore, to calculate the deflection due on this account, but as an illustration we may give this deflection, calculated for the long range attained with the 10-inch gun (5,600 yards), from Captain Boxer's, R.A., Treatise on Artillery. He finds it to be very nearly 11 yards.

Windage, one of the faults, of the spherical bullet, permitting a great escape of the gas, and therefore wasting the force of the powder, has been overcome in various ways in the cylindro-conical picket. The Minié principle consists in hollowing out the base of the ball conically, placing in this hollow an iron cup or piece of wood, which being driven forward by the explosion of the charge further into the conical hollow, enlarges or expands the ball, and makes it fit tight and take the impression of the grooves, though the bullet, when put into the gun, is small enough to be easily rammed down. It is now found that the conical hollow alone, without the cup or plug, is almost equally effective in expanding the ball. We have termed this the Minié principle; Captain Norton, how-over, undoubtedly has a prior claim (which has been allowed by the British Government, we believe) to this invention. He was before his time. There was no cause for, and therefore the shooting mania was not strong upon us.

With breech-loaders, doing away with windage and making the bullet take the rifling, is an easy matter. The breech into which the bullet is put at once, without being passed through the muzzle, is made slightly larger than the rest of the bore; the bullet on being pushed forward by the force of the powder is squeezed into the narrower portion, and effectually prevents all escape of gas. It is thus with the Armstrong gun. Robins said of the breech-loaders of his day, "And, perhaps, somewhat of this kind, though not in the manner now practised, would be, of all others, the most perfect method for the construction of these barrels." Mr. Whitworth, on the other hand, uses -- well, we have avoided details thus far, and every newspaper has described them so fully, that our readers must he thoroughly acquainted with them. Let us conclude, as we began, with Robins, and hope that his prediction that "they," the armies of the enlightened nations which perfect rifles, "will by this means acquire a superiority which will almost equal anything that has been done at any time."