Environmental Shifts and Their Impact on Ammo Performance

If you’re shooting your firearm in an indoor range, you don’t have to worry about weather conditions and altitude. Wherever you happen to be, the controlled environment remains the same.

Such is not the case in the great outdoors, where temperature, humidity and altitude can vary depending on the region of the country and influence both shooting ammo and hunting ammunition performance. 

Temperature and altitude share the ability to impact air density and subsequently ammo performance. Lower altitudes and temperatures produce denser air, creating more drag and drop on the bullet. Conversely, higher altitudes and temperatures cause thinner air, resulting in reduced bullet drag and drop. Generally, a 1,000-foot increase in elevation reduces bullet drop by 1 percent. Higher elevations require less elevation in the scope, while lower altitudes require more elevation.

Temperatures also affect the burn rate of gun powders. As one might expect, given the nature of gunpowder, hotter temperatures produce a faster burn rate and greater velocity. Colder temperatures, on the other hand, result in a slower burn rate and lower velocity. 

Offering some protection against the cold and its effects is the Hodgdon Extreme ammo line and some other newer powders designed to be temperature stable. With these temperature stable powders, the effect of temperature on burn rates and subsequent muzzle velocity is substantially reduced.

The velocity difference varies between different powders. It ranges from less than one foot to two feet per second per degree. With non temperature stable powders, the bullet drops 1 percent for every 10 degrees. Using temperature stable powders, it’s 1 percent for every 20 degrees. 

In the Southeast, where humid weather is the norm, shooters have to account for the less dense air and subsequent greater muzzle velocity at over 1,000 feet by adjusting the rifle scope.