The Effect of Humidity on Small Arms Trajectory

Abstract

With the introduction of handheld electronics, ballistic calculators have become very common. Many smart phone apps and standalone ballistic calculators allow a shooter to calculate the effect of atmospheric changes, along with range and wind, on the trajectory of a projectile. A large majority of these calculation methods utilize a simplified atmospheric model along with simplified trajectory models that reduce the computational burden on the hardware. These models typically ignore the effect of relative humidity on air density. This paper uses a modified 3 degree of freedom (3DoF) point mass trajectory model to examine the sensitivity of a ballistic solution to differences in humidity across multiple temperature ranges. Three common long range shooting calibers are examined across three temperatures. The calibers are .223 Remington, .308 Winchester, and .338 Lapua Magnum. The effect of an accurate humidity measurement on the prediction of the trajectories is shown to be significant. The effect is shown to be dependent strongly on the ambient temperature of the air as well as the target range.