Explosive velocities are always higher than the local speed of sound in the material.
If the explosive is confined before detonation, such as in an artillery shell, the force produced is focused on a much smaller area, and the pressure is significantly intensified.
[1] Typical detonation velocities for organic dust mixtures range from 1400 to 1650 m/s.
In essence, this method relies on the time lag between the initiation of two ends of a detonating fuse of a known detonation velocity, inserted radially at two points into the explosive charge at a known distance apart.
In the cases where a material has not received dedicated testing, rough predictions based upon gas behavior theory are sometimes used (see Chapman–Jouguet condition).