How Guns Were Made to Shoot Straight
In our nursery days we used to try to shoot peas out of small toy cannons, and we were disappointed that we could not shoot straight. Sometimes the toy cannon-ball went one way, and sometimes it went another way. You may be surprised to learn that the real soldiers of not so very long ago had the same trouble with their large cannons, and with their hand-guns, and in their case it was, of course, a much more serious affair.
Listen to what our own gunners reported to the Government in the year 1841, which was the year when the late King Edward was born. The Royal Engineers were asked to make a fair trial of the accuracy of the new musket, the one invented by the clergyman. They had proved already that this percussion-cap musket was very much surer of going off when the trigger was pulled than was the case with any other gun. That would enable the soldier to take better aim, but it did not ensure that the bullet would fly straight to the object at which the soldier aimed.
After the Royal Engineers had given the gun a fair trial, they reported that they had shot at a target which was twice as high and twice as broad as a man, and that with very careful shooting they were only able to hit the target three times out of every four shots, and only if they were fairly near the target: not more than 150 yards away. When they went farther back from the target they could not hit it at all, nor could they even find where the bullets went. Nowadays we are not only sure of hitting the target, but a man who is a "good shot" can hit the very centre mark, which we call the bull's-eye.
If you think of your toy cannon which shot peas, it is not difficult to understand why it could not shoot straight. The pea was such a loose fit for the gun that when it was shot along the barrel of the gun it would go zigzagging along, and whatever side of the barrel it chanced to strike as it left the muzzle, that would determine the direction in which the pea would travel. Sometimes it would go to one side and sometimes to the other; sometimes it would go upwards and at other times it would go downwards. The real guns had the very same fault, and although their bullets were not such very loose fits as the peas for your toy cannon, yet you have seen what very bad shooters the guns were.
The first thing that enabled guns to shoot straight was when the bullets could be put in at the breech end of the gun. The bullet, being made to fit tightly to the bore of the gun, was shot off much straighter than the loose-fitting bullet which had to zigzag its way along the barrel. But there was another very important invention which ensured the bullet flying straight.
You know that the hand-gun of to-day is called a rifle. But why? If you should see a picture of one of Wellington's soldiers with his hand-gun, you would not be right in speaking of his gun as a rifle. Wherein is the difference? The earlier guns had smooth bores through which the bullets travelled along the barrels. The rifle has a grooved bore, a sort of corkscrew, or spiral groove, on the inside of the barrel. The word "rifle" was made up to describe this groove, and the word was made from an old Anglo-Saxon word meaning a groove.
But why do we cut this screw-thread in the bore of the gun? So that when the bullet is forced along the bore of the gun, by the explosion of the gunpowder, the bullet, fitting into these grooves, will spin round and round and leave the muzzle of the gun with a very rapid spinning motion. But what does it matter whether the bullet is spinning round or not as it flies through the air? Ask the old Zulu warrior why, when throwing his assagai, he gives it a spinning motion by means of his fingers and thumb. He does this because he finds that it will travel much straighter through the air. For the same reason the archers used to place the feathers, on the tails of their arrows, at an angle which would cause the arrow to spin round as it flew through the air.
When you walk about on a perfectly calm day you are not conscious that the air offers any resistance to your passage through it. If there is a high wind blowing, you then feel the air rushing past you, and if you are not careful it may carry your hat away with it. Even when the air is perfectly still, it offers a great deal of resistance to a motor-car flying through it at a high speed. Let us make an experiment in our imagination.
We get into a very low motor-car which has a nice sharp nose that can pierce its way through the air. The car has a large wind-screen, behind which we can shelter, but when we set out we leave this screen lying down on the car, ready to put up whenever we wish shelter. It is a perfectly calm day, but by the time the speedometer of the car indicates that we are travelling 35 miles per hour, we have to take care that we do not lose our hats. We can feel the great resistance that the air is offering to our passage through it. We are travelling on a long level road, and the speedometer is standing steadily at 35 miles per hour. I ask you to keep your eye on the speedometer, while I put the wind-screen up in position. You call to me that we are going slower, and yet we have kept the same power on the engine. The indicator of the speedometer soon points to 30 miles per hour; the whole loss of speed is due entirely to the resistance of the air on our wind-screen. If we were to exceed the speed limit to a greater extent, and travel on a racing track at 60 miles per hour, we should find even a greater resistance offered by the air.
Now you will have no difficulty in realising what a great resistance the air must offer to a bullet flying at a speed of 30 miles per minute. Eighteen hundred miles per hour! That is about the speed which a rifle bullet possesses at the moment it leaves the muzzle of the gun, but having to force its way through the air, the bullet falls off in speed very quickly. The first bullets used to be round balls, but the bullet of to-day is long-shaped, and has a pointed nose, as you will see from the accompanying drawing.
I need hardly tell you why this long-shaped bullet was invented. If you think of our imaginary experiment with the motor-car, you will remember that we travelled faster when we had no wind-screen up, the reason being that we did not have such a large surface to force through the resisting air. It must be apparent to you that the sharp-nosed bullet is much better able to force its way through the air than was the clumsy round ball. Therefore the long-nosed bullet of to-day travels faster and farther than the old round bullet.
People did try rifling some of their big guns before these long-shaped bullets were invented. However, the early idea of rifling was not the same as ours, so we need not trouble about these early guns which had the bores made with grooves. We have seen that our idea in rifling guns nowadays is to make the bullets travel straight through the air, without being forced by the air to alter their course. We shall see later that torpedoes have an ingenious arrangement which makes them go straight through the water without altering their course. Meantime you will remember that our idea in giving the bullet a spinning motion is not to make it travel any farther, but to make it go straight; we are doing exactly what the Zulu warrior did with his assagai.
But does the bullet fit into the groove or screw-thread of the bore of the gun, in the same way as a screw-bolt fits into a metal nut? You may be surprised when I say that it does. You say that the bullet has no projecting screw-thread on it, and if you have ever tried to screw a smooth rod of metal into a metal nut, you must have found that it was of no use, as the smooth rod had nothing to fit into the grooves. Indeed, those boys who are fond of working with mechanical things know that a screw-bolt must have exactly the same size of thread before it will fit into a metal nut.
The old-time bullets did have little projections to fit into the grooves in the bore of the gun, and yet our bullets have no such projections. If you have never thought of the matter, you might puzzle a long time before guessing how the modern smooth bullet can possibly fit into the rifled bore of the gun. If I were to tell you that although there are no projections on the bullet so long as it lies idle in your hand, but that there are projections on it just for the moment when it flies along the bore of the gun, you might think I was talking nonsense. A bullet which can possess projections just for a moment, when required, seems to belong to a fairy tale rather than real life. It is a clever invention, and yet extremely simple. This is how it is done.
The bullet is made with a hollow or depression on its end, so when the explosion takes place in the gun, the end of the bullet expands and fits into the spiral groove in the barrel. This turns the bullet round and round as it is forced along the rifle bore. By the time it leaves the muzzle of the gun the bullet is spinning round and round like a top which is spinning very fast. In the case of a shell which is fired from a large gun, there is a soft copper band added round its waist, and when the shell is fired along the barrel this copper is squeezed out so that it fills up the grooves in the bore. So the copper provides the necessary projections to catch in the spiral groove.
The spinning of the bullet is to help it to travel straight, but when a soldier is shooting at a distant object he does not point the muzzle of the gun straight at the object; he points his gun as though the bullet was to pass right over the object. Why? You can easily answer this question yourself, for all boys and girls have some practice in throwing balls to one another. If your playmate is at some distance from you, and you wish to throw a ball to him or her, you throw it high into the air, so that it takes a curved path. Boys sometimes do try to throw a cricket ball in a straight line to a playmate, but only if he is at close quarters. To succeed in doing so the ball must be thrown with great force. Why? So that the ball will not have time to fall to the ground.
It will be quite apparent to you why the gunner shoots his bullets higher than the distant object. He knows that the bullet will tend to fall towards the ground, and so the farther the bullet has to travel, the more time it will have to fall, and therefore the higher he must aim.
It is not left to the soldier to judge how high he must aim. You know that he has "sights" fixed on his gun. These are shown in the accompanying drawing.
The back sight (A) has a little slide on it which can be moved up or down at will. If the soldier moves this slide into a certain position (marked 500 yards), and then looks along his rifle till the slide is in line with the small fixed projection (B), the gun is then tilted the required amount for hitting an object which is 500 yards away. If he raises the slide on the back sight to the point marked 800 yards, it will be evident to you that when he aims to bring the slide in line with the front sight he will, of necessity, tilt the muzzle of the gun still higher. And so the more distant the object, the higher will he raise the back sight, and the higher will the gun shoot.
Suppose for a moment that a soldier is very careless, and that he sets his sight for 1000 yards, while he wishes to shoot at an enemy who is on horseback, and who is already very much nearer him than 1000 yards. What will happen? He pulls the trigger and finds that he has failed to hit the enemy. The soldier guesses that the bullet must have gone right over the enemy's head, so he now aims low at the feet of the horse, thinking to make sure that the bullet will not rise too high this time. But having the sight still set for 1000 yards, the ballet still goes over the enemy's head, as shown in the accompanying drawing.
You will see how important it is to have the sight of a gun properly set for the required distance. You will understand how important it is, also, to get rid of this upward curved path, so far as that is possible. If a bullet would only fly from the muzzle of the gun straight to the distant object, without rising any higher, it would be much more dangerous to the enemy. It would not matter whether or not we knew exactly how far off the enemy was, we should merely have to point the muzzle of the gun straight at him.
How can we get a bullet to fly lower? The boy who threw the cricket ball straight to his companion can tell us what we must do. We must throw the bullet very fast, so that it will have little time to fall to the ground. And so it was that by using a long-shaped, sharp-nosed bullet we were able to get it to travel faster through the air.
The bullets used to be made of lead, but the lead was too soft for rifled guns, as particles of lead were apt to fill up the grooves. A solid steel bullet would be too light, and you know that it is not easy to throw a light object to a distance. This led to the invention of a new kind of bullet. The new bullet was made with a hard nickel-steel jacket with a heavy core of lead within it, and these are the kind of bullets we use to-day.
This small-sized heavy bullet enables our guns to shoot more directly at the distant object without having to throw the bullet so high into the air. We use a big word to describe the path taken by a bullet; we call the path the trajectory. Some boys and girls like big words, and these are always of interest if we inquire into the make-up of the big word. Those who know something of Latin will easily guess the derivation of the word trajectory. It is made up of two Latin words, trans, which means across or over, and jacio, meaning, I throw. In this connection we have the Latin words, trajicio and trajectum. And so our English word trajectory means the path described by an object which is thrown.
When you hear that a certain gun has a very flat trajectory you will understand what is meant, and you will know that the enemy has not much chance of escape. You will remember that we are able to get a flatter trajectory by making the bullet travel very fast, thus giving it less time to fall to the ground. On the other hand, you will remember that we get bullets to travel straight through the air by giving them that quick spinning motion which is obtained by rifling the bore of the gun.
It really does not matter very much whether a rifle can send a bullet 4000 or 5000 yards, so long as it can shoot straight at an object 1000 yards away. The soldier will not likely be asked to fire at an enemy until he is within 1000 yards, and probably not till he is very much nearer.
I was very much amused by the way in which an American writer sought to impress his readers with this point. He wanted them to understand that so long as a bullet could keep a flat trajectory, and thus go straight at an object 1000 yards away, it did not matter what happened to the bullet if it went farther, and this is how he put the matter. "Promise a fighting man a rifle that had a danger zone of 1000 yards, but the bullet of which faded into thin air at 1500 yards, and he'd fall on your neck and call you brother, and probably try to pick your pockets of the plans of the new weapon."