A two‐stage light‐gas gun is used for a variety of dynamic physical‐property measurements at 100 GPa (1 Mbar) pressures. The diagnostic system described here consists of a flash x‐ray system to measure impactor velocity, detectors and electronics to measure shock‐wave velocities with subnanosecond resolution, and data–analysis techniques that permit us to measure the tilt and distortion of the impactor and of the resulting shock front. We describe our methods for safely purging hydrogen gas from the system after each shot.