What substance can affect the performance of primers?

The performance of primers can be significantly affected by penetrating oils. These oils are designed to penetrate and lubricate metal surfaces, which can interfere with the chemical reaction needed for the primer to ignite. When primer materials are contaminated with oils, especially those that do not evaporate quickly, it could lead to misfires or failures to fire because the oil can coat the sensitive components of the primer that are needed to strike and ignite the primer material.

In contrast, while water can damage ammunition if not properly sealed and dried, it does not typically impact the immediate performance of the primer itself in the same way that penetrating oils do. Powder residue can accumulate in firearms and affect overall functionality but does not directly alter the primer. Cleaning agents, depending on their formulation, can actually help clear contaminants but may not specifically affect primer performance unless they leave a residue that inhibits ignition. Therefore, the primary concern with penetrating oils is their potential to obstruct the primer's functionality, making them the correct choice in this context.