What type of ammunition is commonly used in the M9 pistol?

The M9 pistol is specifically designed to fire 9mm Parabellum ammunition, which is also known as 9x19mm. This cartridge is widely used in military applications due to its effective range, manageable recoil, and adequate stopping power, making it suitable for both law enforcement and military personnel. The 9mm Parabellum round strikes a balance between performance and control, allowing for rapid follow-up shots and accuracy, which are crucial in combat situations.

Other ammunition types mentioned, such as .45 ACP, high-velocity .22 caliber, and 5.56 NATO, are not compatible with the M9 pistol. Each of these cartridges serves different purposes and is used in different firearms optimized for their specific ballistics and operational roles. For instance, .45 ACP is typically used in larger caliber handguns, while 5.56 NATO is a rifle cartridge, and high-velocity .22 caliber ammunition is more commonly associated with smaller caliber rifles and handguns. Thus, the 9mm Parabellum is the correct and commonly used ammunition for the M9 pistol.