Abstract An analysis has been developed for the Ballistic Mortar test based on classical mechanics and a two stage chemical reaction rate model. Non-ideal behaviour of the composition was modelled by partial energy release during the detonation phase and secondary exothermic processes during the expansion phase. Erosive grain burning and time delayed reactions were both considered. Gas loss from the mortar cavity due to leakage was included. Predicted mortar performance of several ideal and non-ideal explosives were in good agreement with experimental values. The effects of slow and incomplete reaction of non-ideal compositions have been demonstrated, and it has been shown that measurement of mortar throw angle alone is insufficient to determine the performance of a composition. The model has been used to elucidate the reaction rate behaviour of Ammonium Nitrate and Aluminium in commercial explosives.