Burning samples of nitramine composite solid gun propellants were quenched, and the burned surfaces examined microscopically and by chemical analysis. Studies were carried out on XM39 and M43 propellants, on an HMX-polyester composition (HMX2) and on pure RDX, at pressures ranging from atmospheric (0.1 MPa to 2.0 MPa). Scanning electron microscopy examination of quenched samples burned at these low pressures indicates that a liquefied layer 100 to 300 mu thick forms during combustion of these nitramine compositions. Bubbles are present, especially at the lower pressures, Gas chromatography mass spectrometry analysis suggests that in the case of XM39, ethyl centralite stabilizer is depleted in the surface layers relative to the plasticizer acetyl triethyl citrate. High-performance liquid chromatography studies indicate that for XM39 (and presumably for M43), HMX2, and RDX, the surface layers exhibit formation of the mechanistically significant nitrosoamines MRDX (also known as ONDNTA) and DRDX Examination of the burned surfaces of XM39 and of HMX2 by photoacoustic Fourier-transform infrared spectroscopy and by microreflectance Fourier-transform infrared spectroscopy indicates the presence of increased amounts of binder and its decomposition products. Examination of the burned surface of RDX by photoacoustic Fourier-transform infrared indicates the presence of RDX decomposition products. These observations suggest the occurrence of a significant amount of condensed-phase decomposition. Depth profiling, by surface-abrasion and by cross-section examination, indicates that in the nitramine propellants the molten oxidizer laver is overlain by a layer (similar to 20 mu thick) of binder and its decomposition products. The roles of vaporization and of thermal decomposition in the liquid layers of the nitramine propellants are also discussed; it appears that both play significant roles.