Which component compresses the recoil spring during operation?

The component that compresses the recoil spring during operation is primarily the slide assembly. When the pistol is fired, the force of the bullet being expelled pushes the slide backward, which compresses the recoil spring. As the slide moves rearward, it allows for the ejection of the spent casing and the functioning of the firearm’s cycling mechanism. After the slide has completed its rearward travel, the recoil spring pushes the slide back into position, chambering a new round in the process.

The locking mechanism, firing pin assembly, and unlocking mechanism serve different roles within the pistol's operation. The locking mechanism ensures that the barrel and slide are locked together during the firing sequence, preventing premature unlocking. The firing pin assembly is responsible for striking the cartridge’s primer to initiate firing but does not directly interact with the recoil spring. The unlocking mechanism allows the slide to disengage from the locked position but is not responsible for compressing the recoil spring during operation.

Understanding the function of the slide assembly in relation to the recoil spring is crucial for grasping the M9's operation, as it illustrates the mechanics behind the semi-automatic cycling and reloading process in this service pistol.