A hydraulic rotary-percussive hammer drill comprising: - a body , - a shank intended to be coupled to at least one drill bar equipped with a tool, - a striking piston slidably mounted inside the body along a striking axis (A) and configured to hit the shank , - a stop piston which is slidably mounted in a cavity of the body according to an axis of displacement substantially parallel to the striking axis (A), the stop piston including a front face facing the shank and configured to position the shank in a predetermined balanced position with respect to the striking piston , and a rear face opposite to the front face and located opposite a rear wall of the cavity , and - a high-pressure fluid feed-in conduit and a low-pressure fluid return conduit , the body and the stop piston delimiting at least partially a first control chamber permanently connected to the high-pressure fluid feed-in conduit and configured to urge the stop piston forwards, the stop piston further comprising a connecting channel configured to fluidly connect the first control chamber to the high-pressure fluid return conduit when the rear face of the stop piston is located at a distance from the rear wall of the cavity which is larger than a predetermined value, the body and the stop piston further delimiting at least partially a second control chamber configured to urge the stop piston forwards, characterized in that the hydraulic rotary-percussive hammer drill comprises a fluidic communication channel which opens into the second control chamber and which is configured to supply the second control chamber with high-pressure fluid, the fluidic communication channel being provided with a calibrated orifice . - a body , - a shank intended to be coupled to at least one drill bar equipped with a tool, - a striking piston slidably mounted inside the body along a striking axis (A) and configured to hit the shank , - a stop piston which is slidably mounted in a cavity of the body according to an axis of displacement substantially parallel to the striking axis (A), the stop piston including a front face facing the shank and configured to position the shank in a predetermined balanced position with respect to the striking piston , and a rear face opposite to the front face and located opposite a rear wall of the cavity , and - a high-pressure fluid feed-in conduit and a low-pressure fluid return conduit , the body and the stop piston delimiting at least partially a first control chamber permanently connected to the high-pressure fluid feed-in conduit and configured to urge the stop piston forwards, the stop piston further comprising a connecting channel configured to fluidly connect the first control chamber to the high-pressure fluid return conduit when the rear face of the stop piston is located at a distance from the rear wall of the cavity which is larger than a predetermined value, the body and the stop piston further delimiting at least partially a second control chamber configured to urge the stop piston forwards, characterized in that the hydraulic rotary-percussive hammer drill comprises a fluidic communication channel which opens into the second control chamber and which is configured to supply the second control chamber with high-pressure fluid, the fluidic communication channel being provided with a calibrated orifice . <EOS>