The principle used to zero firearms is the parabola. If you connect the front sight and the rear sight, the two points form a line, and the bullet's trajectory is a parabola. The line extending from the two points of the front sight and the sight can have two intersections with the parabola of the bullet. Generally speaking, the process of clearing is to set the distance at which the bullet coincides with the line of the front sight and the rear sight.
In the current habit, the distance between the bullet and the line of sight for the first time is generally called the zero distance.
Many of the military's shooting training is at a distance of 100m. The reason is that most of the assault rifles have bullets that coincide with the line of sight at a distance of 100m. Another coincidence distance is 300m, but the bullets at a distance of 300m are affected by wind and the spread area will be large, and the shooting range at a distance of 300m will occupy a much larger area than a shooting range at 100m.
The distance to zero can actually be set by yourself. Generally speaking, the distance between the bullet and the line of sight of the rifle can be between 75m and 150m. The pistol is special. Although all pistols are basically designed with an effective distance of about 50m, then a person standing at 50m and an outsider can use the naked eye to see the size of a rice grain, plus the pistol’s short aiming baseline and pistol bullet The speed is slow and so on. Generally pistols are factory-set to zero distance, of course, different calibers and different bullets are not the same.
As for the situation of returning to zero at 1000 meters and hitting 100 meters, it will basically not happen. First of all, there will be no guns to set the distance between the bullet and the line of sight for the first time at 1000 meters. It is the 0.338 caliber with the longest effective range at present. The 0.408 caliber and 0.416 caliber are generally set at about 700 meters to zero.
As for setting the zero return distance of 1000m, it means that the bullet is set to coincide with the line of sight at 1000m. Before 1000m, the bullets are theoretically flying below the line of sight. In fact, the distance between the bullet and the line of sight is not too far. Take the 95 rifle that has been hacked for example, the aiming baseline is only 60mm, that is to say, set 1000m to zero and design a distance of 100m even if the shooter does not make any adjustments when aiming, the bullet will be several centimeters lower than the aiming point. The trained archer will definitely have a margin when aiming, and aim a little higher when aiming.
