Manual of Military Training Part 110

Sights and Sighting

_Theory of Sighting_

=1349. The trajectory.= As the bullet pa.s.ses through the air it makes a curved line something like this:

[Ill.u.s.tration: Fig. 1]

This curved line is called the _trajectory_.

The resistance of the air and the force of gravity (the force that pulls all bodies toward the earth) are the two things that make the path of the bullet a curved line, just the same as they make the path of the baseball thrown by the player a curved line.

The resistance of the air holds the bullet back and the force of gravity pulls it down, so that the two acting together make the bullet's path curved.

The longer the range the more will the path of the bullet (the trajectory) be curved, as shown by the following drawing:

[Ill.u.s.tration: Fig. 2]

=1350. Sighting or aiming.= Now, on the rifle there are two "sights,"--the _front sight_ and the _rear sight_,--which enable the rifleman to regulate the path of the bullet, as the ball player regulates the path of the ball.

If the ball player wants distance, he throws the ball high (raises the path, the trajectory), using his eye and guesswork, and likewise if the rifleman wants to shoot at a distant target, he, too, shoots the bullet high (that is, he raises the muzzle of his rifle), but he doesn't have to depend upon guesswork. It is all worked out for him by experts and all he need do is to set the _rear sight_ for the proper range,--that is, for the distance the object is from him.

Aiming or sighting a rifle consists in bringing into line three objects: _The target_, A, _the front sight_, B, and _the rear sight_, C.

[Ill.u.s.tration: Fig. 3]

The rifle is so made and the sights placed on it in such a way that when the piece is held in such a position that the _target_, the _front sight_ and the _rear sight_ are in line, and the trigger is pulled (squeezed) the bullet will strike the _target_.

You raise the muzzle of the piece by raising the rear sight,--that is, raising the rear sight has the effect of raising the muzzle, for the higher you raise the rear sight the higher must you raise the muzzle in order to see the front sight and get it in line with the object aimed at and the rear sight.

This is shown in the following ill.u.s.trations:

[Ill.u.s.tration: Fig. 4]

[Ill.u.s.tration: Fig. 4a]

The rear sight, C, the front sight, B, and the bull's eye, A, are all on a line with the eye, D, the rear sight being set for 200 yards.

Suppose we wanted to shoot at 2000 instead of 200 yards. We would raise the slide up to 20 (2000 yards) on the sight leaf.

In order to see the bull's eye through the notch sight at 2000, we must raise the eye to the position, D. We now have the rear sight, the bull's eye and the eye in line, but we must bring the front sight in line with them, which is done by raising the muzzle of the piece, giving the result shown in Fig. 4a.

=1351. Line of sight.= With the open sight the line of sight is determined by a point on the middle line of the notch of the rear sight and the top of the front sight.

With the peep sight, the line of sight is determined by the _center_ of the peep and the top of the front sight.

Kinds of sights

=1352.= (See Fig. 3, par. 1343, giving rear sight leaf in detail.)

The different kinds of sights are as follows:

(a) =Open sight.= By _open sight_ is meant the use of any one of the _sighting notches_.

To use the open sight:

1. Look through the sighting notch at the target. (Fig. 5.)

[Ill.u.s.tration: Fig. 5]

[Ill.u.s.tration: Fig. 6]

2. Bring the top of the front sight _on a line with the top and in the center_ of the sight notch, _the top of the front sight being just under the bull's eye_.

Because of its wide field of view and its readiness in getting a quick aim with it, the open sight is the one that is generally used in the later stages of battle, or when fire is to start immediately.

(b) =Peep Sight.= By _peep sight_ is meant the use of the _peep hole_ in the drift slide.

To use the peep sight:

1. Look through the peep hole at the target. (Fig. 7.)

[Ill.u.s.tration: Fig. 7]

2. Bring the top of the front sight to the _center_ of the peep hole, _the top of the front sight being just under the bull's eye_. (Fig. 8)

[Ill.u.s.tration: Fig. 8

_Correct_]

_Be sure to get the top of front sight_, as in Fig. 8, _and not the bull's eye_, as in Fig. 9, _in center of the peep hole_.

[Ill.u.s.tration: Fig. 9

_Incorrect_]

=Advantage of the peep sight.= The advantage of the peep sight over the open sight is due to the fact that it is easier to center the top of the front sight in the peep hole and thus get the same amount of front sight each time.

For example you know at once, without measuring, that the dots in the circles, Fig. 10, are not centered, and that the one in the circle in Fig. 11, is.

[Ill.u.s.tration: Fig. 10]

[Ill.u.s.tration: Fig. 11]

After a little practice, in looking through the peep hole the eye almost automatically centers the top of the front sight.

=Disadvantage of the peep sight.= The disadvantage of the peep sight is that its limited field of view and lack of readiness in getting a quick aim with it limit its use to those stages of the combat when comparative deliberation will be possible.