Setting tool containing a laval nozzle

A setting tool employing an explosive caseless propellant charge for driving fastening elements into a hard target material, comprises a member forming an axially elongated bore having a rear end and a front end, said member forming a combustion chamber arranged to receive a caseless propellant charge and said combustion chamber located adjacent the rear end of said bore and on the opposite side of said rear end from the front end thereof, said member forming at least one gas flow channel communicating between said combustion chamber and the rear end of said bore, a drive piston movably displaceable through said bore from the rear end toward the front end thereof under the action of an exploded propellant charge and said drive piston being movably displaceable toward the rear end of the bore after the insertion of a fastening element, wherein the improvement comprises that said gas flow channel is a Laval nozzle, and an axially extending firing pin located within said member rearwardly of said combustion chamber for igniting a propellant charge therein.