However, on earth there is air resistance. As the bullet falls air resistance will cause the bullet to stop accelerating and hit terminal velocity (terminal velocity is the speed at which air resistance balances the accelerating force of gravity). Experiments have determined that falling bullets reach terminal velocity at 200-300 feet per second depending on type. Note that falling bullets (shot vertically) usually do not come down nose first – which would be the most aerodynamic – but instead tumble, which really slows the bullet.
When you fire a bullet into the air, it typically takes between 20 and 90 seconds for it to come down, depending on the angle it was fired at, its muzzle velocity and its caliber. So, if you are a bystander, you have some time to take cover.