When should you replace the barrel of the M9 pistol?

The barrel of the M9 pistol should be replaced when pitting exceeds one land in width and 3/8 inch in length. This measurement is crucial because excessive pitting can significantly affect accuracy and reliability. Pitting can create uneven surfaces that affect the bullet's trajectory and can also lead to further corrosion or failure during operation. By establishing precise criteria for barrel replacement, such as the dimensions given, the user ensures that the weapon continues to function effectively and safely.

Discoloration alone does not necessarily indicate that a barrel is beyond safe use, as it may not affect performance. Worn rifling is indeed a concern, but the specific criterion of pitting exceeding the defined dimensions provides a tangible measurement that can be assessed visually and physically. Additionally, replacing the barrel after a predetermined number of rounds, such as 500, does not take into account the actual condition of the barrel – every weapon may wear differently based on how it is used and maintained. Thus, relying on pitting criteria not only ensures a higher standard of performance but also addresses safety concerns directly related to the integrity of the barrel.