A hydraulic piston-cylinder group includes a cylinder containing a piston which defines internally of the cylinder at least a first and a second chamber, respectively communicating with a first and a second inlet/outlet hole of a pressurized fluid for actuating the piston between a first and a second position. The piston has a gully defined by a bottom wall, a first lateral wall that is proximal to the first free end, and a second lateral wall distal relative to the first free end, the first and second lateral walls serving as first and second abutments for the piston ring, the gully communicating through at least a passage with the first chamber. A depression is provided on the contact surface between the second lateral wall of the gully and the piston ring, the depression enables a controlled bleeding of the pressurized fluid between the piston ring and the second lateral wall.