Which component assists in both locking and releasing the slide of the M9 service pistol?

The component that assists in both locking and releasing the slide of the M9 service pistol is the slide stop. This part plays a crucial role in the operation of the firearm by engaging with the slide during the cycling process. When the pistol is fired and the last round is ejected, the slide stop engages with the slide, holding it in the open position. This is beneficial for the shooter to visually confirm that the magazine is empty and also prepares them for a quick reload.

When a new magazine is inserted, the shooter can release the slide by either pulling back on the slide and letting it go or by pressing the slide stop, which allows the slide to move forward into battery, chambering a new round. This dual functionality makes the slide stop essential for both maintaining proper operation and facilitating quick reloads, enhancing the overall user experience and efficiency when operating the weapon.