What environmental factor can cause parts of a firearm to freeze in position?

Moisture is the environmental factor that can lead to parts of a firearm freezing in position. When moisture comes into contact with the metal components of a firearm, especially in cold temperatures, it can lead to the formation of ice. This ice can cause moving parts, like the action or trigger, to become stuck or fail to operate properly. Additionally, wet conditions can lead to rust and corrosion over time, which can further impair the functionality of the firearm.

While factors such as high temperature, wind chill, and humidity can influence firearm performance, they do not directly cause components to freeze like moisture can. High temperatures can lead to overheating, wind chill affects perceived temperature but does not add moisture, and humidity relates more to moisture content in the air, which by itself does not cause freezing but can contribute to the moisture problem. Thus, moisture is the key factor directly influencing the freezing of firearm components.