A high-speed photographic study has been performed of the initiation mechanisms of hexanitro-hexaaza-isowurtzitane (CL-20) and nitrotriazolone (NTO) by drop-weight impact. CL-20 was found to be slightly more sensitive and · NTO less sensitive than cyclotetramethylene tetranitramine (β-HMX) in our drop-weight apparatus. NTO was found to be sensitised by both hard high-melting point grits (60 μm borosilicate or pyrex glass) and brittle polymers. Heat-sensitive film was used to confirm that the events seen using high-speed photography were indeed deflagration.