An experimental study was made of the shock wave projected into free water from the end of a hydrodynamic conical shock tube driven by a high explosive. Pressure‐time measurements were made with small piezoelectric and piezoresistive gauges arrayed about two different shock tube configurations. For one tube, designed on a very small scale, results showed that a remnant of the sector shock front propagated undisturbed over the length of the water tank (20 cone lengths). This was demonstrated by the fact that attenuation with distance along the extended cone axis closely approximated the accepted relationshipP∝R−1.13for explosion shock waves in free water. On‐axis data for the other tube whose shock wave energy was three orders of magnitude greater than the first, showed very rapid attenuation beyond the cone mouth. Both cone results are consistent with existing theory that defines the undisturbed shock front region in terms of cone parameters—length, angle, and amount of explosive—that affect shock energy and geometry. Results for the first cone on attenuation of pressure with angle to the axis also were consistent with the predicted angular extent of the undisturbed front region. At 30°, attenuation was about 75%.