Abstract: Apparatus for compacting and advancing a mass of particulate or fibrous material to a discharge end of a conduit combines an auger with a reciprocating annular piston. The improvement of the invention is in driving the piston by way of a flywheel equipped crankshaft which also drives a dynamically counter balancing member to reduce vibrations transmitted to the frame of the apparatus. Special hydrostatic guide sleeves are used to guide the reciprocating piston at a high speed. Further improvements include gas and liquid vents and a cooling jacket, both associated with the conduit to increase efficiency of the compacting. A density sensor controlled conical choke member at the discharge end assists in maintaining uniform density of the highly compacted plug of the material. Also, it breaks up the exiting plug to improve subsequent processing of the material.