In the context of the M249 AR, which round is not used for mechanical training?

The M249 Automatic Rifle (AR) uses specific rounds designed for various training purposes. The round that is not utilized for mechanical training is the M856 API (Armor-Piercing Incendiary). The M856 is specifically designed for combat scenarios where penetrating armor is necessary, combining armor-piercing capabilities with an incendiary effect.

Mechanical training typically focuses on rounds that allow operators to practice loading, unloading, and cycling the weapon without the risks associated with live or specialized ammunition. In contrast, dummy rounds (like the M199) and blank rounds (like the M200) are explicitly used for mechanical and tactical training purposes, as they do not pose the same hazards as rounds designed for active combat use. The M855 is a standard ball round used for live fire exercises, while the M856 is oriented toward offensive operations rather than training. Therefore, the M856 API is the appropriate choice since it is meant for different operational contexts and does not align with mechanical training objectives.