Which gauge is utilized to inspect the M240B machine gun for barrel erosion?

The correct choice involves using both the muzzle and breech bore wear gauge to inspect the M240B machine gun for barrel erosion. This gauge is specifically designed to assess the condition of both ends of the barrel, allowing for an accurate evaluation of erosion and wear caused by the firing of ammunition over time.

Inspecting both the muzzle and breech is essential because erosion can occur at different points along the barrel due to the intense heat and gases produced during firing. The muzzle wear gauge measures erosion at the muzzle end, while the breech wear gauge focuses on the chamber area where the cartridge is seated. By using a combined assessment tool, the evaluator can get a comprehensive view of the barrel's integrity, which is crucial for maintaining the weapon's performance and safety.

The other choices focus on either end of the barrel separately or provide ambiguous terms that do not typically correspond to standard gauges used for checking erosion on a machine gun barrel.