Sometimes a man does not know how to place the eye in the line of sight; he will look over or along one side of the notch of the rear sight and believe that he is aiming through the notch because he sees it at the same time that he does the front sight. Again some men in sighting will look at the front sight and not at the object.

Repeat the above exercise, using the _peep_ sight. If aiming correctly, the rear sight, the front sight and the bull's-eye will look as shown in Fig. 20.

[Ill.u.s.tration: Fig. 20]

Second Sighting Exercise

=1359. The triangle of sighting.= Using the sighting rest for the rifle as before (Fig. 17), direct the marker to move the disk until the rifle is directed on the bull's-eye with the _normal_ sight and command "Mark," whereupon the marker, being careful not to move the disk, records through the hole in its center, the position of the disk, and withdraws it. Then, being careful not to move the rifle or sights repeat the operation until three marks have been made.

Join the three points by straight lines. The shape and size of the triangle will indicate the nature of the variations made in sighting.

[Ill.u.s.tration: Fig. 21]

For example, if you have taken the same aim each time, you will get a very small triangle something like this: [Ill.u.s.tration: triangle]

which resulted from taking each time this aim, for instance:

[Ill.u.s.tration: Fig. 22]

A triangle like Fig. 22 results from not taking the same amount of front sight each time, as shown in Fig. 23.

[Ill.u.s.tration: Fig. 23]

[Ill.u.s.tration: Fig. 24]

A triangle like Fig. 24 shows that the front sight was not in the middle of the notch each time, as shown in Fig. 25.

[Ill.u.s.tration: Fig. 25]

A triangle like Fig. 26 results from a combination of the two errors mentioned above,--that is, not taking the same amount of front sight each time and not having the front sight in the middle of the notch each time, as shown in Fig. 27.

[Ill.u.s.tration: Fig. 26]

[Ill.u.s.tration: Fig. 27]

If any one of the sides of the triangle is longer than one-half inch, the exercise is repeated, each sight being verified by the instructor, who will call the soldier's attention to his errors, if any.

The smaller the triangle, the better the sighting.

=1360. Verifying the triangle.= If the sides of the triangle are so small that they indicate regularity in sighting, mark the center of the triangle and then place the center of the bull's-eye on this mark.

The instructor then examines the position of the bull's-eye with reference to the line of sight. If the bull's-eye is properly placed with reference to the line of sight, the soldier aims correctly and with uniformity.

If the bull's-eye is not properly placed with reference to the line of sight, the soldier aims in a regular manner but with a constant error.

=1361. Causes of errors.= If the bull's-eye is directly above its proper position, the soldier has aimed high,--that is, he has taken too little front sight.

If the bull's-eye is directly below its proper position, the soldier has aimed low,--that is, he has taken too much front sight.

If the bull's-eye is directly to the right or left of its proper position, the soldier has not sighted through the center of the rear notch and over the top of the front sight. If to the _right_, the soldier has either sighted along the _left_ of the rear sight notch or the _right_ side of the front sight, or has committed both of these errors.

If the bull's-eye is to the _left_ of its proper place, the soldier has probably-sighted along the _right_ of the rear sight notch, or to the _left_ of the front sight, or has committed both of these errors.

If the bull's eye is diagonally above and to the right, the soldier has probably combined the errors which placed it too high and too far to the right.

Any other diagonal position would be produced by a similar combination of vertical and horizontal errors.

After the above instruction has been given to one man, the line of sight will be slightly changed by moving the sighting rest or by changing the elevation and windage, and the exercises similarly repeated with other men.

Repeat the exercise, using the _peep_ sight.

Third Sighting Exercise

=1362.= This exercise shows the effect of canting the piece.

It is most important that in aiming the sights be kept vertical and the piece not be canted,--that is, that the barrel be not tilted over to the right or left.

If the piece is canted to the right, the sights are lowered to the right and consequently the bullet will strike to the right and below the point aimed at, even though the rifle be otherwise correctly aimed and the sights correctly set.

Similarly if the piece is canted to the left the sights are lowered to the left, and consequently the bullet will strike to the left and low.

This effect of canting the piece may be shown as follows: Use the sighting rest with the rifle firmly held in the notches, the bolt removed.

Paste a black paster near the center of the bottom line of the target.

Sight the rifle on this mark, using about 2000 yards' elevation. Then, being careful not to move the rifle, look through the bore and direct the marker to move the disk until the bull's-eye is in the center of the field of view and command, "Mark."

Next, turn the rest (with the rifle) over 90 to the right, on its side, and with the same elevation, sight on the same paster as above.

Then, being careful not to move the rifle, look through the bore and again direct the marker to move the disk until the bull's-eye is in the center of the field of view and command, "Mark."

Not considering the fall of the bullet, the first mark represents the point struck with the sight vertical, the second mark represents the point struck, low and to the right, using the same elevation and the same point of aim, when the piece is canted 90 to the right.

Different degrees of canting the piece can be represented by drawing an arc of a circle through the two marks with the paster as a center.

The second mark will be at a point on this arc corresponding to the degree of canting the piece.

It is important to know that this effect of canting increases with the distance from the target.

Fourth Sighting Exercise

=1363.= This exercise is to show the advantage of blackened sights.

In strong sunlight, make a triangle of sighting, using a rifle having sights worn bright. Then, being careful not to move the rifle, blacken the sights and make another triangle.

Use dotted lines for the triangle with bright sights and full lines for the triangle made with blackened sights.

The position and size of the two triangles will plainly show the advantage of using blackened sights.