Which of the following components is not included in the major component groups of the M9 service pistol?

The major component groups of the M9 service pistol include the receiver assembly, slide assembly, and frame assembly. Each of these groups plays a significant role in the overall operation and functionality of the firearm.

The receiver assembly houses key parts of the firing mechanism and the operating system. The slide assembly contains crucial components such as the barrel and recoil spring, which are vital for the semi-automatic operation of the pistol. The frame assembly provides the structural foundation for the firearm, integrating with the other assemblies to facilitate handling and shooting.

The trigger assembly is a critical component but is more accurately described as a subgroup within the larger component groups and not a major group on its own. While it is essential for the operation of the pistol, it does not fit the definition of a major component group in the same way as the other three. Understanding these components and their roles is vital for proper maintenance, operation, and effective use of the M9 service pistol.