Amorphous Co_Fe_Si_B_ alloy powders prepared by a cavitation method were dynamically compacted by using a propellant gun. The compacts retained amorphism when they were formed under shock pressures below 8GPa. The highest degree of compaction gave a density of 7.67 Mg/m^3 or 99.6% of that of the amorphous ribbons. After proper heat-treatment, the compact of 0.13mm thick gave a coercive force of 10mOe and a permeability at 100Hz of 12000. Further annealing in rotating magnetic field was found to make the permeability higher. An evident effect of powder size on the soft magnetic properties of compacted powders was also found
