A gun for dispensing bone cement from a cartridge includes a casing, a cradle for supporting a cartridge containing bone cement, the cradle attached to the casing, a drive rod movably mounted to the casing, the drive rod having a forward end for acting against a piston integral with the cartridge and pushing the piston away from the casing, and a linkage assembly. The linkage assembly includes a trigger pivotally mounted to the casing, and a drive rod advancement member disposed in the casing, the drive rod advancement member being connected to the trigger to be actuated by the trigger and, upon trigger actuation, engage the drive rod so as to advance the drive rod against the cartridge piston. The linkage assembly further includes a first link pivotally mounted to said casing and adapted to engage the drive rod advancement member, a second link adapted to interconnect said trigger and said first link, wherein said second link moves upon the pivoting of said trigger so that the second link movement results in movement of the first link that actuates the drive rod advancement member, a third link movable by a control member between a disengaged position and an engaged position in which the third link links the trigger to the drive rod so that the movement of the trigger is transferred through said third link to the drive rod so that said drive rod advances at a higher speed than when said first link actuates said drive rod advancement member.
