Shock waves are common in interstellar molecular clouds and protostellar cores. It has been suggested that they can release certain molecular species, some of astrobiological importance, that have been locked away and hidden by dust grains within these environments. The ability of shocks to process the gas and dust entrained within them is crucially dependent on the structure of the shock, which, in turn, is dependent on whether the shock is of C ("continuous") type or J ("jump") type. Using a multifluid magnetohydrodynamics code, it has been shown that, in clouds with a population of grains that have a single, uniform radius, the critical speed for the C-to-J shock transition occurs at a speed significantly less than previously calculated, due to the loading of grains on magnetic field lines and the resultant effect that has on the propagation speed for signals in a dusty plasma.