How do temperature and humidity affect ballistics?

Temperature and humidity play significant roles in influencing air density, which in turn affects a projectile's performance. As temperature increases, the density of air decreases, making it thinner. This reduced density allows a projectile to travel with less air resistance, thereby potentially increasing its velocity and altering its trajectory. Conversely, high humidity adds moisture to the air, which can slightly decrease density as water vapor is less dense than dry air. This interplay between temperature, humidity, and air density can significantly affect the ballistics of a projectile, impacting factors such as range, accuracy, and energy retention.

In contrast, the other options do not accurately reflect the effects of temperature and humidity on ballistics. They do not increase the weight of the projectile, and they certainly do affect trajectory rather than having no effect at all. While barrel temperature can be influenced by shooting frequency and environmental conditions, it is not a direct consequence of temperature and humidity affecting ballistic performance in terms of air density.