Abstract <p>The effect of the particle size of oxidant (potassium nitrate) powder on the combustion behavior of a model energetic condensed system has been assessed experimentally by a noncontact microwave method in the pressure range 0.5–40 MPa. We have studied a model composition based on epoxy resin as a combustible binding agent, potassium nitrate, and ferric oxide (Fe₂O₃) as a combustion modifier. In evaluating the experimental linear combustion speed, random errors have been taken into account. Fitting the data with power law and linear functions, we have obtained analytical relations for the linear combustion speed of model energetic condensed systems as a function of pressure. The results demonstrate that, as the particle size of the oxidant powder decreases, the pressure at which the behavior of the combustion speed changes from a power law to linear also decreases, which is accompanied by an increase in combustion speed.</p>