The United States Army Marksmanship Unit Training Manual

6. All the movements of the eyeball, as well as the holding of its fixed position at moments when the glance is fixed on some object, are effected by the work of three pairs of eye muscles. During the time when the eyes are at work, including the times when the eye is aiming, these muscles are in a state of indiscernible, slight vibration or quivering. For example, when aiming a pistol and the shooter turns his head down and to the right, the eyeball turns respectively upward and inward, it is held in the least desirable position; one that requires the combined, intensified work of all three groups of muscles (Figure A2-8). When the eye muscles become fatigued, the involuntary quivering of the eyeball increases considerably and this lessens the accuracy of aiming. Therefore, the shooter must devote major attention to the position of his head when firing. He must select that firing stance in which the head position is the most natural one, with the least amount of tilt, so that the shooter does not look at the target from under his eyebrows or sideways. This results in the rapid fatigue of the eye muscles and, hence, the lessening in the accuracy of aiming.

Figure A2-8. Muscles of the Right Eye. Arrows Show the Direction in which the Eyeball turns when the Muscles designated by the numbers are contracted.

The shooter is interested chiefly in the degree of the eye’s differentiating sensitivity and its resultant sharpness of vision, as well as the degree of accuracy of aiming which the eye can guarantee.

1. Basically, sharpness of vision depends upon the physical properties of the anatomy of the eye. The physical condition of the eye determines primarily the greater or lesser accuracy of the image of the object upon the retina. Those anatomical and physiological conditions determine how well we can see the object. The sharpness of the image upon the retina is the impression received by the brain.

2. Sharpness of vision is usually determined by the minimum space that we are able to see between two objects. In order for this space to be visible, it is necessary for at least one retinal element lying between the images of those two points to be stimulated. Thus, the normal sharpness of vision is generally considered to be that at which the eye can distinguish between two visible points at an angle of one minute.

3. However, the anatomical dimensions of the retinal elements (the rods and cones) do not completely determine the limit of visual acuity. Therefore, the visual acuity of the normal eye actually can be considerably greater than the medical norm. Research works have shown that the average visual acuity of the normal human eye, at one hundred yards under normal illumination, can distinguish distance between objects separated from one another within the limits of 40 angular minutes. This means that the normal eye can distinguish sufficiently clear, for example, a space of .1 inch between the side of the front highs and vertical inside surface of the rear sight notch on the pistol sight at a distance of one yard (the approximate distance to the muzzle and front sight). But the eye of an experienced shooter can distinguish a considerably smaller space between two objects. A number of experiments carried out by specialists attest to the greater accuracy of a trained shooter’s sharpness of vision. For example, the vertical space between front and rear sight against a white background can be discerned down to the minute width of .01 inch.

4. Many experiments confirm that the sharpness of vision can be considerably increased by means of exercises. This increase in the sharpness of vision is achieved by searching for new signs, new criteria for recognizing the form of objects. Such a sign for shooters is undoubtedly their highly developed sense of symmetry and visual memory.

5. Visual Memory: Therefore, in order to achieve symmetry, a visual memory of correct sight alignment, with its symmetrical interrelationship of the front and rear sights, mainly, the equal amount of space between each side of the front and rear sights and the levelness of their horizontal surface must be ingrained into the mind and never violated. No shot should be fired with less than perfection. All these factors, together with an existing sharpness of vision, will provide for accurate and consistent aiming and the accurate calling of the shot.

6. Calling of the shot: Accurate calling of a shot is dependent upon exact recall of the mental image of the sight alignment at the instant of firing. As demonstrated, the presence of 1/100th of an inch error in sight alignment will result in approximately a 3 inch error from target center at 50 yards. Acute awareness of the slightest degree of error in alignment is an absolute requirement of accurate shot calls from a clear visual memory. The overwhelming majority of shooters try to see the front sight sharply, and thus accept the blurring of the bull’s eye. With the passage of time and with regular practice, the eye develops the ability to obtain the identical space relationship between the front sight and the rear sight and with increasing frequency can position the sights uniformly in the center of the aiming area which is blurred and out-of-focus.

Eventually, the shooter develops his visual powers to such an extent that the eye will consistently perform the act of aiming automatically and he can call his shots without error.

7. Changing degrees of accuracy: When the eye performs intensified work, not only the motor apparatus of the eye, but also its light-sensory apparatus has reduced efficiency. When the glance is fixed steadily upon some object, the eye possesses its greatest sharpness of vision for the first several seconds, after which the sharpness of the image on the retina, that is, the clear seeing of it, gradually decreases. Consequently, the shooter must not be captivated by excessively prolonged aiming, since, after the elapse of 12-16 seconds, his eye ceases to notice certain inaccuracies in aiming. By relying on the false assumption that the rear sight and front sight are in correct relationship to one another, the shooter makes grievous errors without noticing and therefore, does not know why they were committed.

a. If one calculates the time between the moment when the visual attention is concentrated on obtaining the precise alignment of the front and rear sights and the moment when the shooter makes the decision to positively press the trigger, the aiming process must not exceed 6-8 seconds.

b. When aiming, some shooters run their eye from the front sight to the rear sight notch and then to the third object, the target, doing this quickly several times, until these three points are all located on the same line. It must be said that his method of aiming causes rapid fatiguing of the muscular apparatus of the eye and fails to provide a constant objective for the formation of a visual memory. With this method of aiming it is very difficult for the shooter, for example, to conduct rapid fire, which is very limited in time. He simply does not have time to run his eye back and forth between objects located at varying distances. The shots may be fired when he is focused on any of the three objects. Consistently accurate shot calls are impossible. Therefore, when aiming, the shooter must strive to see only the front sight sharply and distinctly.

ASSEMBLY AREA is a designated zone in the rear of the firing line, approximately 25 yards, where the next relay of competitors can complete their preparations for the match and receive instruction and advice from their coach or team captain.