The instrumented drop weight impact machine is one possible candidate for establishing the hazard response of solid rocket propellants to impact. The plastic work done on the propellant prior to initiation can be measured by equating it to the loss in drop weight kinetic energy, provided energy storage in the machine is negligible. Three HTPB/AP propellants were studied with an instrumented impact machine. Data are given for impact velocities ranging from 5.54 m/s, at which no sample was consumed, to 16.14 m/s, at which nearly all of the sample was consumed. These data are interpreted in terms of a proposed mechanism based on other impact tests. On bare steel tools ignition, as opposed to hot spot formation, is assumed to occur at impact velocities greater than 10.3 m/s, when more than 90% of the sample is consumed during the test. At higher impact velocities, for the present data, times to reaction are short and the change in impactor kinetic energy during the initiation delay is defined as the critical initiation energy. Some of the trends in the data are correlated with the propellant formulations. The present test is contrasted with others suggested for impact sensitivity characterization in terms of both initiation threshold and response severity.