What is one of the four main conditions requiring boresight?

Boresighting is a critical procedure in firearms and optics to ensure that the aiming point of a weapon aligns with the point of impact. One of the main conditions requiring boresight is a hard landing. This event can lead to misalignment of the weapon system, particularly in aircraft where vibrations and impacts from landing can shift the positioning of the optic or the weapon itself. Consequently, a thorough boresight is essential to reset the alignment and ensure that the weapon functions correctly, accurately, and safely after such incidents.

In contrast, weapon malfunctions, routine maintenance, and long-term storage may not necessarily require immediate boresighting. Malfunctions can sometimes be resolved without the need to realign the sights, while routine maintenance often focuses on cleaning and inspection rather than alignment checks. Long-term storage might require a general check-up, but not always an immediate need for boresighting unless there are specific issues detected during that time. Thus, a hard landing provides a clear and pressing reason to conduct boresighting to regain the necessary precision in the weapon's operation.