Flying bullets: the basics of sniper case
The naked eye can seem like an optical sight on a rifle barrel parallel. In fact it is not.
The axis of the barrel and the optical axis of the sight form an angle, called the angle of sight. And the trajectory of the bullet, of course, not straight, and the target is not always on the same level with a rifle - often have to shoot at great angles of elevation or declination.
During the flight to operate bullet gravity and various aerodynamic forces that need to be taken into account when aiming.
gravitation
Effect of gravity on the flight of the bullet is evaluated fairly simple. For some time (or at a certain distance) bullet decreases and the decrease depending on shooting distance can be calculated by the ballistic calculator or tables, and then amended with a suitable sight of the flywheel.
As a rule, flywheels are graded in the corners - the West adopted angular minutes (minutes of angle, MOA), in Russia - thousandths of the distance, or mrad (transverse dimension of 1 m at a distance of 1000 meters, 1 mrad = 3.43 MOA) .
To facilitate the sometimes calibrated in meters distance flywheels problem (such amendment will operate under standard conditions for a specific munition).
Distance
The correct definition of distance is essential for accurate shooting.
To do this, there are many techniques - the use of a laser rangefinder reticle or comparison with the known dimensions of the main subjects to accept the type of "man's hands and feet movement distinguishable from 500-600 meters."
There are also a number of situations that make it difficult to correct the visual determination of the distance. The greater the shooting distance, the greater the error in determining the distance will affect the final result - the ability to hit a target.
Wind
Air resistance slows flying bullet, and this must be taken into account in the calculation of the amendments (especially in unusual situations - for example, in mountainous areas, where the air is thin). It affects as humidity and air temperature. But much more important is the aerodynamic demolition bullet crosswind.
The fact is that during firing at long distances (several hundred meters) along the bullet trajectory can change the wind several times - both in strength and direction. The city high-rise buildings create a powerful air flows seriously hamper the work of police snipers during special operations.
The speed and wind direction must be determined by fluctuations updraft - mirage - or even at all anticipate. Sniper proverb says: "Members learn ballistic tables and skilled snipers - the wind."
Derivation
The point of application of force of gravity to the pool (the center of mass) does not coincide with the point of application of the aerodynamic forces (pressure center is located in front of the center of mass). As a result of these forces occurs overturning moment in the trajectory of the plane.
However, since the bullet is rotating and the gyro, its axis of rotation perpendicular to the plane deviates. That is, if the bullet rotates to the right, there is a deviation to the right and there is a precession - fluctuations in the rotation axis of the bullet. The axis of precession will be denied the right, aerodynamic forces deflect the bullets flying in the same direction.
This phenomenon is called derivation. It depends on the speed of the bullet and its rotational speed, mass and shape. Usually, this effect begins to affect the accuracy of shooting only at sufficiently large distances (where it is likely "lost" against the background of a much greater wind drift).
Magnus effect
For instance, it is worth considering shooting adjusted for angle field goal. This situation is found in the mountains or in the city, where snipers equipped with a position on the roofs of buildings.
When firing at a target located above or below the arrow, it is necessary to make a correction, which depends on the elevation angle, but does not depend on whether it is positive or negative angle - in both cases, when administered to a conventional bullet corrections held above the target. Shooting at an angle to the horizon requires the introduction of amendments less than usual.
The fact that the absolute decline in the trajectory of a bullet to the trunk line is always considered perpendicular to the horizon, and the relative decline (the trajectory of a bullet in the line of sight) - perpendicular to the line of sight.
Through the glass
Quite often, the police snipers faced with a situation where the terrorists who seized the hostages, is behind the transparent barrier - glass. Aim it is possible, but would be possible to get there? It would seem that the glass - a fragile material, but it can significantly affect the result of the shooting. This snipers through express a few thoughts.
Firstly, it all depends on the thickness and glass material. Secondly, do not use hollow point bullets inclined while passing through solid obstacles to change the trajectory of an unpredictable manner. The third shot is perpendicular to the glass has less influence on the trajectory of the bullet.
Some types of windows provide many sharp pieces that can harm not only terrorists but also hostage. Often the method is applied when one of the police snipers shot breaks the glass, and his colleagues, almost without pause, hit the target.
The shoot?
Properties cartridge and bullets in the sniper case mean nothing less than the dignity of the trunk or sight. Therefore, speaking about high-precision small arms, we mean "rifle-ammunition" system. There are many types of ammunition for sniper rifles, different caliber, cartridge length, bullet design and characteristics of gunpowder charge, but a real "workhorse" should recognize the cartridge caliber .308 Winchester, also known as 7,62 NATO.
It is the cartridges "of match" class, produced by precision equipment with minimal tolerances. Bullets used in this type of ammunition, refer to the acronym BTHP (Boat-Tail Hollow Point). The term boat-tail ( «boat feed") denotes a characteristic conical tail part of the bullet. Tail cone decreasing lead of the bullet, thereby improving its aerodynamic characteristics, and reduces the loss rate increases resistance to lateral wind.
The bullet also has a cavity in the head part (hollow point) - it enhances the lethal effect. 168-grain bullets sniper .308 Winchester caliber bullet manufactured Remington BTHP companies, Hornady, Lapua, Norma, Federal, and others. In fact also used sniper caliber rounds .223, .300, and even a half-inch caliber .50 (for large-caliber rifles).
Energy saving
Usually snipers using special ammunition design "of match" class. But sometimes you have to work with other types of bullets, the properties of which it is important to consider when shooting. Bullets "brittle" type in contact with the purpose disintegrate into tiny fragments, which penetration is very small. Almost 100% of energy is transmitted bullet purpose.
These bullets were created specifically for security agents accompanying flights. Hitting the terrorists, "fragile" the bullet does not pass right through and in case of accidental contact is not able to break through the fuselage of the aircraft or injure others.
Expansive bullets on target "disclosed" by giving up to 70% of energy, which also reduces the risk of bleed. Bullet cartridge of general purpose due to its shape gives the smallest amount of energy (about 50%). The risk of passing right through, in this case is quite large.
Tips sniper
1. The barrel must not come into contact with anything! 2. Press the trigger to be the most sensitive part of the pad of the index finger. 3. To set the position of the bed is put under the butt of sack with sand. Pushing it free hand shooting, you can fine-adjust the height. 4. It is precisely to maintain a distance between the eye and the eyepiece to completely and without distortion to see all the visual field. Typically, this value is 7? 10 cm. 5. If time permits, it is necessary to fix the position of a rifle with a strap. 6. Avoid stalling weapons. 7. As better not to use fully native fry, and a sandbag.
Ammunition "of match" class to maximize the capabilities of high-precision sniper rifles require increased accuracy of munitions, the so-called class of match ammunition. They are manufactured on high-precision equipment with minimal tolerances. Special attention should be paid to the design of the bullets. It is distinguished by a conical tail portion in the form of "boat stern" and filled the cavity with lead in the bow of the shell.
Breathe and shoot Breathing is important not to disturb the stable position of the rifle. Therefore correct to carry out a shot on the exhale, with the lung devastated when the sniper can "freeze" for a few seconds. To extend the pause between breaths, the shooter must twice a deep breath before firing, to saturate the blood with oxygen. However, when seconds count, the sniper may not be enough time for two deep breaths. Then apply the technique of "hardening" - with light, filled halfway or three-quarters.
Driving firing at an angle to the horizontal dashed line shows the absolute reduction bullets at a given distance. Without making specific amendments to the bullet will fall above the target.
According to the ballistic curve Gravity acts on the flying bullet in the same way as any falling object. During the flight of the bullet is significantly reduced, which may lead to slip. The decline can be calculated from tables or by using a ballistic calculator, but it is necessary to accurately determine the distance.
Train your eye estimation! Good old "thumb method" allows you to quickly estimate the distance
There are a number of situations where visual identification of distance, even a trained eye can give an error. In some cases, objects may appear closer: in a valley hidden behind the hills, when you look from top to bottom, along the long straight landmarks such as rails or a contrasting uniform background like snow or sand. In other cases, the objects may appear further away than they actually are located: on a background of large objects and structures, when viewed from the bottom up in the narrow space in the visible or valley.
Via popmech.ru
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