Reduced sensitivity RDX (RS-RDX) particles are now available from several manufacturers. But a clear understanding of this reduced sensitivity behavior is not yet available. RS-RDX particles are usually employed in cast formulations to reduce their shock sensitivity. The use of RS-RDX in pressed formulations is more recent and does not always give reduced sensitivity formulations. Pressed and cast ISL formulations have been processed with RS-RDX lots and usual RDX lots. These formulations exhibit various kinds and amounts of pores, but they are all composed of 70% in weight of RDX and 30% of the same wax. The shock sensitivity of these formulations has been measured using the 20 mm projectile impact experiment. The different roles of the various kinds of pores are pointed out. It seems important to distinguish the pores inside the RDX particles (intra-granular pores), the pores in the bulk of the inert binder (extra-granular pores), and the pores at the interface between the RDX particles and the inert binder (interface pores). The effects of the pore sizes are outlined. It is experimentally demonstrated that RS-RDX particle lots can be used to process reduced sensitivity pressed formulations. The reduced shock sensitivity of the ISL pressed formulations is effective even with an amount of five volume percent of extra-granular pores.