A syringe for injecting solid, hard and rough granular material, having diameters comprised between 0.1 and 1.5 mm, comprising: a longitudinal injection chamber (10) having constant section and an internal diameter (Dc) of less than 4.5 mm, having a distal outlet mouth (1 1 ) for the flow out of the material, whose surface is the same as the injection chamber (10), and a proximal mouth (12), in which granular material is inserted; a plunger (20) sealedly mobile along the injection chamber (10), joined to a stem (21 ) which enters the injection chamber (10) through the proximal mouth, the plunger (20) having a transversal section which sealingly couples with the surface of the injection chamber (10), and having an operative surface (22), facing towards the distal mouth (1 1 ) of the injection chamber (10), suitable for pushing the material along the injection chamber (10), characterised in that it comprises a body (24) projecting longitudinally internally of the injection chamber (10), fixed substantially axially to the operating surface (22) of the plunger (20), having a diameter (Ds) that is less than 70% of the diameter (Dc) of the injection chamber (10) and a length (Ls) that is greater than 6 mm.