A delivery gun for discharging bone cement from a cartridge that includes a piston. The gun has a casing from which a drive rod and a disk extend. A drive assembly advances the drive rod and disk so that disk displaces the piston causing the discharge of cement. The drive assembly includes plural links that are pivotally connected to a trigger. The links are displaced in response to the manual displacement of a trigger. One of the links is configured to selectively engage the drive rod. When this particular link is engaged with the drive rod and displaced, the drive rod the drive rod is advanced at a first speed. When this link does not is not engaged with the drive rod, the drive rod is advanced by another link at a second speed.