Flying bullet: the basics of sniper
To the naked eye it may seem that the optical sight on the rifle is parallel to the barrel. In fact, it is not.
The axis of the barrel and the optical axis of the sight form an angle, which is called the aiming angle. And the trajectory of the bullet, of course, not straight, and the goal is not always on the same level with a rifle - often have to shoot with significant angles of elevation or declination.
In flight on a bullet, gravity and various aerodynamic forces act, which must be considered when aiming.
The effect of gravity on the flight of a bullet is quite simple. At a certain time (or at a certain distance), the bullet decreases, and this decrease depending on the firing distance can be calculated using a ballistic calculator or from tables, and then corrected using an appropriate sight handwheel.
As a rule, flywheels are graded in the corners - angular minutes (minutes of angle, MOA) are used in the West, 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 graded in meters of distance (such an amendment will work for a particular ammunition under standard conditions).
Correct determination of the distance is extremely important for accurate shooting.
For this, there are many techniques - from using a laser rangefinder or comparing an aiming grid with known dimensions of objects to basic ones such as “movements of a person’s arms and legs are distinguishable from 500-600 m”.
There are also a number of situations that impede the correct visual determination of distance. The greater the firing distance, the greater the error in determining the distance will affect the final result - the possibility of hitting the target.
Air resistance slows down the flying bullet, and this must be taken into account when calculating corrections (especially in unusual situations - for example, in mountainous conditions, when the air is thin). Humidity and air temperature are also affected. But much more important aerodynamic demolition bullet side wind.
The fact is that when firing over long distances (several hundred meters) along the bullet's flight path, the wind can change several times - both in strength and in direction. High-rise buildings in the city create powerful air currents that seriously impede the work of police snipers during special operations.
The speed and direction of the wind has to be determined by the fluctuations of the ascending air currents - mirages - or even completely predicted. A sniper saying reads: "Beginners learn ballistic tables, and seasoned snipers - the wind."
The point of application of gravity to the pool (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, an overturning moment arises in the plane of the trajectory.
But since the bullet rotates and is a gyroscope, its axis of rotation is deflected perpendicular to the plane. That is, if the bullet rotates to the right, a deviation to the right occurs and a precession occurs - oscillations of the axis of rotation of the bullet. The axis of this precession will be rejected to the right, aerodynamic forces deflect the flight of a 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. Typically, this effect begins to affect the accuracy of firing only at fairly large distances (where it is likely to be “lost” against the background of a much more significant demolition by the wind).
As a separate case, it is worthwhile to consider shooting adjusted to the elevation angle of the target. This situation occurs in the mountains or in the 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 an amendment, which depends on the elevation angle, but does not depend on whether it is positive or negative, in both cases, when a normal amendment is introduced, the bullet passes above the target. Shooting at an angle to the horizon requires the introduction of an amendment less than usual.
The fact is that the absolute decrease in the trajectory of a bullet to the trunk line is always considered perpendicular to the horizon, and the relative decrease (the trajectory of the bullet flying to the line of sight) is perpendicular to the line of sight.
Through the glass
Quite often, police snipers have to deal with a situation where a terrorist who took 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. Snipers express several considerations on this score.
First, it all depends on the thickness and material of the glass. Secondly, you should not use expansive bullets that are prone to change the trajectory in unpredictable ways when passing through solid barriers. Thirdly, a shot perpendicular to the glass has less effect on the trajectory of the bullet.
Some types of glass give a lot of sharp fragments that can harm not only the terrorist, but also the hostages. Often the method is used when one of the police snipers smashes the glass with a shot, and his colleagues almost without a pause hit the target.
What to shoot?
The properties of the cartridge and bullet mean in the sniper business no less than the advantages of the barrel or sight. Therefore, speaking of high-precision small arms, we mean the system “rifle-ammunition”. There are many varieties of ammunition for sniper weapons, differing in caliber, cartridge length, bullet design and powder charge characteristics, but the .308 Winchester cartridge, also known as 7.62 NATO, should be recognized as the “workhorse”.
We are talking about the cartridges of the “match” class, produced on precision equipment with minimum tolerances. The bullets used in this type of ammunition, denoted by the English abbreviation BTHP (Boat-Tail Hollow Point). The term boat-tail (“boat feed”) denotes the characteristic conical tail of a bullet. The tail cone, reducing the leading part of the bullet, thereby improves 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 action. 168-sided sniper cartridges of .308 Winchester caliber with a BTHP bullet are manufactured by Remington, Hornady, Lapua, Norma, Federal, etc. The sniper case also uses cartridges of .223, .300 and even half-inch .50 caliber (for large-caliber rifles).
Usually snipers use special “match” class ammunition. 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 are in contact with the purpose of scattering into small fragments, the penetrating ability of which is very small. Almost 100% of the bullet energy is transferred to the target.
Such bullets were created specifically for security agents accompanying flights. Hitting a terrorist, the “fragile” bullet does not go right through and, if accidentally hit, is not able to pierce the aircraft’s fuselage or injure those around it.
Expansive bullets when hit the target "open", giving up to 70% of energy, which also reduces the risk of destruction through. The bullet from the general purpose cartridge due to its form gives the least amount of energy (about 50%). The risk of going through a hole in this case is quite high.
1. The barrel should not touch anything! 2. Pull the trigger should be the most sensitive part of the pads of the index finger. 3. To set the position of the bed is to put a bag of sand under the butt. By pressing on it with a free hand, it is possible to make a fine adjustment in height. 4. It is necessary to accurately maintain the distance between the eye and the eyepiece so that you can see the entire visual field completely and without distortion. Usually this value is 7 × 10 cm. 5. If time permits, it is necessary to fix the position of the rifle with the help of a belt. 6. Do not stall the weapon. 7. As an emphasis it is better to use not a regular bipod, but a bag with sand.
Ammunition "match" class To maximize the capabilities of high-precision sniper rifles require high-accuracy ammunition, the 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 cavity not filled with lead in the bow part of the shell.
Breathe and Shoot When breathing, it is important not to disturb the stable position of the rifle. Therefore, it is more correct to perform a shot while exhaling, with the lungs emptied, when the sniper can “freeze” for a few seconds. In order to prolong the pause between breaths, the shooter must inhale two times deeply before the shot to saturate the blood with oxygen. However, when the count goes on for a second, the sniper may simply not have enough time to take two deep breaths. Then apply the technique of "freezing" - with light, filled in half or three quarters.
Firing scheme at an angle to the horizon. The dashed line shows the absolute decrease in the bullet at a given distance. Without special amendments, the bullet will fall above the target.
According to the ballistic curve, Gravity 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. The reduction can be calculated from the tables or using a ballistic calculator, but you need to accurately determine the distance.
Train your eye! Good old "thumb method" allows you to quickly estimate the distance
There are a number of situations in which the visual determination of distance even by a trained eye can give an error. In some cases, objects may appear closer: in a low, hidden behind hills, when viewed from top to bottom, along long straight landmarks such as rails or on a contrasting uniform background such as snow or sand. In other cases, objects may appear farther than they are actually located: against the background of large objects and structures, when viewed from the bottom up, in a narrow space or in a visible lowland.