The flight of bullets: the basics of sniping
It may seem to the unaided eye that the optical sight on the rifle is parallel to the trunk. In fact, this is not so.
The axis of the barrel and the optical axis of the sight form an angle, which is called the angle of sight. And the bullet trajectory, of course, is not direct, and the target is not always on par with the rifle - often you have to shoot with significant angles of elevation or declination.
In flight, bullets are acted upon by gravity and various aerodynamic forces that must be taken into account when aiming.
The influence of gravity on the flight of a bullet is fairly simple. For a certain time (or at a certain distance), the bullet is reduced, and this decrease, depending on the shooting distance, can be calculated with a ballistic calculator or on tables, and then corrected with the help of a corresponding flywheel of the sight.
As a rule, flywheels are graduated in corners - in the West, angular minutes are taken (minutes of angle, MOA), in Russia - thousandths of a distance, or milliradians (transverse size of 1 m at a distance of 1000 m, 1 mrad = 3.43 MOA) .
To facilitate the task, flywheels are sometimes graduated in meters of distance (such an amendment will work for a specific munition under standard conditions).
The correct determination of the distance is extremely important for accurate shooting.
To do this, there are many methods - from using a laser rangefinder or comparing a sighting grid with known sizes of objects to the main signs such as "the movement of the arms and legs of a person are distinguishable from 500-600 m".
There are also a number of situations that make it difficult to correctly determine the distance. The longer the shooting distance, the greater the error in determining the distance will affect the final result - the possibility of hitting the target.
Air resistance slows the flying bullet, and this must be taken into account when calculating corrections (especially in unusual situations - for example, in mountainous terrain when air is rarefied). The humidity and air temperature also influence. But much more important is the aerodynamic demolition of the bullet by the side wind.
The fact is that when shooting at long distances (several hundred meters) along the trajectory of a bullet, the wind can change several times - both in force and direction. In the city, high-rise buildings create powerful airflows, seriously hampering the work of police snipers during special operations.
The speed and direction of the wind have to be determined by the fluctuations of the ascending air currents - mirages - or even completely anticipate. The sniping proverb says: "Beginners learn ballistic tables, and seasoned snipers are the wind."
The point of application of gravity to the bullet (center of mass) does not coincide with the point of application of aerodynamic forces (the center of pressure, located in front of the center of mass). As a result of these forces, a tipping moment appears in the plane of the trajectory.
But since the bullet rotates and represents a gyroscope, its axis of rotation deviates perpendicular to the plane. That is, if the bullet rotates to the right, a deviation to the right occurs and precession arises - the oscillations of the axis of rotation of the bullet. The axis of this precession will be deflected to the right, the aerodynamic forces reject the flight of the bullet in the same direction.
This phenomenon is called derivation. It depends on the speed of the bullet and the speed of its rotation, mass and shape. Usually this effect begins to affect the accuracy of shooting only at sufficiently large distances (where it is most likely "lost" against the background of a much more significant drift by the wind).
The Magnus Effect
As a separate case it is necessary to consider shooting with the correction for the angle of the target's place. This situation occurs in the mountains or in a city where snipers equip positions on the roofs of buildings.
When firing at a target that is above or below the arrow, it is necessary to make a correction, which depends on the elevation angle, but does not depend on whether the angle is positive or negative - in both cases, when the conventional correction is introduced, the bullet will pass above the target. Shooting at an angle to the horizon requires the introduction of a correction less than usual.
The fact is that the absolute decrease in the trajectory of the bullet to the line of the trunk is always considered to be perpendicular to the horizon, and the relative decrease (the trajectory of the bullet to the aiming line) is perpendicular to the aiming line.
Through the glass
Quite often, police snipers have to face the situation when a terrorist who has taken hostages is behind a transparent barrier - glass. You can aim at it, but will you manage to get there? It would seem that glass is a fragile material, but it can significantly affect the result of shooting. In this regard, snipers have several thoughts.
First, it all depends on the thickness and material of the glass. Secondly, do not use expansive bullets that are prone to traversing through rigid obstacles to change the trajectory in an unpredictable manner. Thirdly, a shot perpendicular to the glass less affects the trajectory of the bullet.
Some types of glass give a lot of sharp fragments, which can harm not only the terrorist, but also the hostages. Often a method is used when one of the police snipers fired a shot at the glass, and his colleagues beat the target almost without pause.
Than to shoot?
The properties of the cartridge and bullets in the sniper business mean as much as the advantages of the barrel or sight. Therefore, speaking of high-precision small arms, we mean the "rifle-ammunition" system. There are many types of ammunition for sniper weapons, differing in caliber, cartridge length, bullet design and powder charge characteristics, but a true "workhorse" should be recognized cartridge .308 Winchester, also known as 7.62 NATO.
It's about the "match" class cartridges produced on precision equipment with minimal tolerances. The bullets used in this type of ammunition are designated by the English abbreviation BTHP (Boat-Tail Hollow Point). The term boat-tail ("boat feed") refers to the characteristic conical tail of the bullet. The tail cone, reducing the leading part of the bullet, thereby improving its aerodynamic characteristics, reduces the loss of speed and increases the resistance to the side wind.
The bullet also has a cavity in the head (hollow point) - this enhances the killer effect. 168-grained sniper cartridges of the .308 Winchester caliber with the BTHP bullet are manufactured by Remington, Hornady, Lapua, Norma, Federal, etc. The sniper case also uses cartridges of .223, .300 caliber and .50 caliber .50 calibers (for large-caliber rifles).
Usually snipers use ammunition of a special design of the "match" class. But sometimes you have to work with other types of bullets, the properties of which are important to consider when shooting. The bullets of the "fragile" type, when in contact with the target, are scattered into small fragments, the punching capacity of which is very small. Almost 100% of the bullet energy is transmitted to the target.
These bullets were created specifically for the security agents that accompany the flights. Shocking a terrorist, a "fragile" bullet does not pass through, and if accidentally hit, it can not penetrate the fuselage of an aircraft or injure others.
Expansive bullets hit the target "open", giving up to 70% of the energy, which also reduces the risk of damage to the rifle. The bullet from the general-purpose cartridge, due to its shape, gives the least amount of energy (about 50%). The risk of passing through in this case is quite large.
Tips for the sniper
1. The trunk must not come into contact with anything! 2. Press the trigger follows the most sensitive part of the cushion of the index finger. 3. To set the position of the bed it is necessary to put a sandbag under the butt. Pressing on him free from shooting by hand, you can make a fine adjustment in height. 4. It is necessary to withstand exactly this distance between the eye and the eyepiece in order to see the whole visual field completely and without distortion. Usually this value is 7 × 10 cm. 5. If time permits, it is necessary to secure the position of the rifle with a belt. 6. Do not allow the dumping of weapons. 7. As an emphasis it is better to use not a regular bipod, but a bag of sand.
Ammunition of the "match" class For maximum implementation of the capabilities of high-precision sniper rifles, ammunition of increased accuracy is required, so-called cartridges of the match class. They are manufactured on precision equipment with minimum tolerances. Particular attention should be paid to the design of the bullet. It is distinguished by a conical tail part in the form of a "boat stern" and a lead-free cavity in the nose of the shell.
Breathe and shoot When breathing, it is important not to disturb the stable position of the rifle. Therefore, it is best to perform a shot on exhalation, with emptied lungs, when the sniper can "freeze" for a few seconds. To prolong the pause between the breaths, the shooter must take two deep breaths before the shot to saturate the blood with oxygen. However, when the score goes for a second, the sniper may simply not have enough time for two deep breaths. Then the technique of "hardening" is applied - for light, half-filled or three-fourths.
Scheme of shooting at an angle to the horizon The dashed line shows the absolute decrease in the bullet at a given distance. Without making any special corrections, the bullet will hit above the target.
On a ballistic curve, Gravitation acts on a flying bullet in the same way as on any falling object. During the flight, the bullet is significantly reduced, which can lead to a miss. Reduction can be calculated from tables or using a ballistic calculator, but you need to accurately determine the distance.
Train your eye! The good old "thumb method" allows you to quickly assess the distance
There are a number of situations in which a visual definition of distance, even by a trained eye, can give an error. In some cases, objects may seem closer: in the lowlands hidden behind the hills, when viewed from top to bottom, along long straight landmarks such as rails or on a contrasting uniform background like snow or sand. In other cases, objects may appear further than they actually are: against the background of large objects and structures, when viewed from the bottom up, in a narrow space or in a visible lowland.