What must you do each time you replace the bolt or slide of a gas-operated firearm?

When replacing the bolt or slide of a gas-operated firearm, it is essential to check the headspace. Headspace refers to the measurement from the part of the chamber that stops the forward movement of the cartridge to the point where the case will rest. Proper headspace ensures that the ammunition fits correctly in the chamber, which is crucial for the safe and reliable operation of the firearm.

If the headspace is too short, it can lead to difficulties in chambering the round, while excessive headspace can result in problems such as misfires or dangerous situations like case separation. Since the bolt or slide is integral to the functioning of the firearm, any change can affect the headspace. Therefore, verifying this measurement after replacing these components is a critical step in ensuring the firearm's safety and functionality.

Regularly inspecting magazine condition, calibrating sights, and cleaning the barrel are also important firearm maintenance tasks, but they do not directly relate to ensuring the precise fit and function of the bolt or slide in relation to the chamber. Hence, the focus on checking the headspace is both standard practice and necessary for maintaining the operational integrity of gas-operated firearms.