Nitramines are known to produce lower burning rates and higher pressure exponent (?) values. Studies on the burning rate and combustion behavior of advanced high-energy NG/PE-PCP/HMX/AP/Al based solid propellant processed by slurry cast route were carried out using varying percentages of HMX and AP. It was observed that propellant compositions containing only AP and Al loaded (total solids 75?%) in NG plasticized PE-PCP binder produce comparatively lower pressure exponent (?) values similar to AP-Al filled HTPB based composite propellants. However, energetic propellants containing high level of nitramine (40-60?%) produce high pressure exponent (0.80.9) values in the same pressure range. Incorporation of fine particle size AP (ca. 6 mu m) and change in its concentration in the propellant composition reduces ? value marginally and influences the burning rate. However, such compositions have higher friction sensitivity.