What must be maintained while locking the bolt to the rear during a function check?

When locking the bolt to the rear during a function check, maintaining positive control of the cocking handle is essential. This ensures that the bolt remains securely in the rearward position and prevents it from unintentionally moving forward. Positive control implies that the operator must hold the cocking handle firmly to manage and stabilize the bolt's position effectively.

This practice is crucial for safety, as it prevents the bolt from closing unexpectedly, which could lead to injury or accidental discharge if a round were to be chambered. Proper technique not only ensures a thorough and safe function check but also affirms the user’s control over the firearm during maintenance and inspections.