Which sub-component of the M9 service pistol is responsible for locking the slide rearward?

The slide stop is the sub-component of the M9 service pistol that is responsible for locking the slide rearward. When a magazine is empty, the last round fired triggers the slide stop to engage, holding the slide in a rearward position. This feature allows the shooter to recognize that the pistol is empty and makes it easier to reload. The design ensures that the slide does not move forward unless the slide stop is deliberately disengaged, typically by pressing the slide release.

The slide release, while closely related, serves a different purpose; it is used to release the slide back into battery after a reload rather than locking it back. The recoil spring's function is to return the slide forward after firing, and the firing pin is responsible for striking the primer of a round to ignite it, making them unrelated to the locking function. Thus, the slide stop is the critical component in ensuring the slide remains locked in the rearward position after the last round, enhancing safety and operational awareness.