I’m sure everyone here knows that a bullet is most effective when it’s traveling through the air at its prescribed velocity. After all, that’s what the bullet is designed to do. The cartridge holds the powder, and once the powder ignites, initiated by the primer, the projectile unseats from the casing, travels the length of the barrel, and goes about its merry way. But let’s not forget the final factor to consider before the projectile strikes home—its “happy place,” the air.

Over the course of the projectile’s short airborne life, what are its ideal living conditions? Here is a short breakdown of what a projectile likes as it exits the end of your rifle barrel. This brief analysis of the significance of ambient air density will hopefully give you a better understanding of environmentals that you’ll be able to apply every time you hit the range. Be sure to track the data over time and look at the differences from engagement to engagement, analyzing the weather.

Bullet Ambient air density

Ambient air density is classified into four categories: air temperature, barometric pressure, humidity, and density altitude.

Air temperature: As the air temperature rises, the air density is lowered. Because there is less resistance, the velocity of the round will increase, causing the point of impact to rise. Note that this is in relation to the air temperature at which the rifle was zeroed. If you were to zero your rifle when the air temperature was 60 degrees, but fire the rifle in a temperature of 100 degrees, the point of impact will rise considerably.

Barometric pressure: Barometric pressure is often referred to as atmospheric pressure, and is the force that is exerted on objects by the weight of the atmosphere above them. Though we may think of gas as not weighing on anything, it does, in fact, have mass. Because of this and the effect of gravity upon the gas itself, the air above us and around us does weigh down on us, and will in the same manner on a bullet.

The barometric pressure is measured in the downward force that the atmosphere exerts per unit of measure in a certain given area. In the realm of precision shooting, the air pressure is less at higher altitudes and the air is less dense. This means that the bullet is more efficient due to having less drag.