An investigation of the projectile impact sensitivities of single, double and triple base propellants is described. The tests were conducted by firing different diameter, flat-ended brass projectiles into small cylinders of the propellant at various velocities and observing the impact reaction by appropriate sensors. It is shown that at large projectile diameters the impact velocity threshold for inducing detonation in the propellants is higher than for inducing burning (sustained ignition); whereas at small diameters the induced reaction is only detonation. These results are similar to those obtained earlier on a deflagratable composite explosive. They support the general validity of a previously postulated model, which was based on the view that the ignition and reaction buildup in an impacted propellant are independent processes.