A fireman having a recoil spring, a recoil spring plug and a barrel bushing for directing and transferring recoil forces from a slide to a slide-supporting receiver of the firearm utilizes a lockplate inserted transversely through the slide and interposed between the barrel bushing and the recoil spring plug. The lockplate maintains the recoil spring plug and barrel bushing within the slide and allows transference of recoil forces from the slide to the recoil spring. The slide defines a through-aperture and both the barrel bushing and the recoil spring plug define a slot positionable in registry with the slide through-aperture so as to define an opening extending transversely through the firearm. The recoil spring plug is movable forwardly and rearwardly to a limited extent relative to the slide, and when the recoil spring plug is depressed in its rearward position and the barrel bushing is rotated into appropriate registry with the slide, the lockplate is insertable through the defined through-opening. When the recoil spring is released to its forward position, the lockplate is prevented from being withdrawn from the through-opening, thus securely locking both the barrel bushing and the recoil spring plug within the slide.