When a gun is shot in the air, the bullet travels straight up into the sky and it will keep moving up until the initial kinetic energy of the bullet is exhausted as a result of air resistance and gravity then it attains its maximum height.
It is at that point that the bullet starts falling to the ground at a terminal velocity that is lower than the muzzle velocity when it left the barrel of the gun. When the bullet starts falling where it will land might be unpredictable because of the effect of air and wind on it, nevertheless, these falling bullets can injure people and kill people.
It should be noted that when a gun is shot at an angle that is less than vertical, it is more dangerous when falling because the bullet maintains the angular ballistic trajectory and the chances of its engaging in a tumbling motion is less, which makes it travel at a speed that is higher than a bullet that is in a free fall.
A falling bullet can reach a speed of more than 61 metres per second and a bullet that is travelling at a speed of 46 to 61 metres per second can penetrate the skin, if it goes faster than this it can penetrate the human skull.
For instance, a pointed bullet moves slower when falling, however, it can still penetrate the human skin, whereas a hollow point bullet is much lethal and this is not because it is easy for it to penetrate the human skin but when they do they create more damage to the human skin.