Many people have this question. Whether it is a pistol, an automatic rifle, a sniper rifle or a machine gun, the sights are all installed above the barrel, but why the bullet hits the aiming point when shooting, not at the aiming point What about below?



First of all, unlike many people's intuition, when the shooter shoots a target at the same level as himself, the barrel is not actually horizontal, but has a slight upward angle. If you can't understand, we might as well assume what happens when the barrel is absolutely horizontal:



If the barrel is in an absolutely horizontal state, when the bullet is moving in the barrel and has not exited the muzzle, it will be accelerated by the thrust of the gunpowder gas in the horizontal direction, and at the same time it will be subjected to the gravity of the earth in the vertical direction, but at this time there is a force on the wall of the barrel. The support in the vertical direction and the elastic force provided by the barrel wall balance each other, so it can be ignored. After the bullet flies out of the muzzle, the bullet flies by inertia and no longer accelerates; it is affected by gravity in the vertical direction, and there is air resistance at the same time, so the trajectory of the bullet is roughly a flat throwing motion.





It's like dropping an aerial bomb on a plane flying horizontally



So for the gun, it means that as soon as the bullet leaves the muzzle, it starts to fall, lower than the horizontal aiming line, and the bullet will definitely fall below the aiming point, and the farther the distance is, the greater the amount of downward deviation is, which is obvious Missed the target. Therefore, when shooting, the barrel of the barrel is actually lifted slightly upwards, and the trajectory of the bullet after flying out of the muzzle is not a straight line, but a parabola. It's just that the slight lift is so small that you don't feel it.





In this picture, the black line is the trajectory of the bullet, and the red line is the aiming axis, which is the extension line of the eye-sight-sight-target



Since the bullet is flying in a parabola, it must rise first and then descend. In the above picture, the bullet coincides with the aiming line at 200 meters. That is to say, if the target is at 200 meters, the bullet can hit the aiming point after shooting.



So what if the target is at 100 meters? The point of impact will be 8 cm higher.



What if the target is at 300 meters? will be 30 cm lower.



We all know that the shooting target cannot always be at a distance of 200 meters, it can be far or close, so how can the gun ensure that it can shoot targets at different distances within the effective range, and the impact point will fall on the aiming point, not too high or too low? It can be imagined from the trajectory of the bullet ejection that if you want to shoot a target at a distance of 300 meters, then the muzzle must be raised higher than in the picture, that is, when shooting a target at a distance of 200 meters, so that the upward angle of the bullet flying out of the muzzle is greater Larger and throw farther, so that when the bullet falls, it will meet the aiming line at 300 meters and hit the aiming point. If you want to shoot a 100-meter target, let the muzzle lift angle be lower, the upward angle of the trajectory of the bullet flying out should be smaller, and throw it closer, so that when the bullet falls, it will meet the line of sight at a distance of 100 meters, and aim at the target. point.



But how can the muzzle lift angle be higher and lower? This requires a gauge.





M1918A2 Automatic Rifle Scale Stand Standing Up



The picture above is the American M1918A2 automatic rifle with the gauge erected, which is the familiar BAR automatic rifle. You can see that there are numbers on both sides of the scale frame, which are arranged alternately from bottom to top, from 1 to 15. There is also a YD lettering on the top of the scale frame, which stands for yard, and its meaning is 100 yards to 1500 yards, every 100 yards. . At present, the cursor of the rear sight is at the lowest position of the gauge, which is 100 yards. Suppose now that you want to shoot a target at 500 yards, move the cursor of the rear sight up to the scale 5. The position of the rear sight is high. If the barrel is still level state, then when looking forward from the rear sight hole, the line of sight passes above the sight of the muzzle, and the sight is invisible.




After raising the rear sight cursor, if the barrel does not lift up, the front sight cannot be seen from the rear sight hole, and the line of sight passes above the front sight.




To aim from the sight hole to the front sight, the butt of the gun must be lowered and the muzzle raised slightly so that the front sight falls into the sight of the sight hole. It's just that this movement is so small that you don't notice it.




To aim at the front sight from the rear sight hole, the muzzle of the gun must be lifted upwards before the front sight enters the field of vision, and the muzzle is raised at an angle.



At this time, the muzzle of the gun is raised, and when the bullet flies out of the muzzle, the angle of upward throw is greater, and it can fall at a distance of 500 yards to meet the line of sight and hit the aiming point. The digital scale on the gauge plate is not engraved blindly, it is engraved after calculation based on the angle of muzzle lift of this gun when shooting targets at different distances, so the gauge plate is to quantify the action of "lifting the muzzle up to a certain angle" Tool of.