The detonation products of high explosives are dependent on pressure and also on the confinement under which the detonation reaction proceeds. To determine the detonation products of less sensitive high explosives such as INT/nitroguanidine (NQ) and PBX charges with polyhutadiene (PB) binder containing RDX together with or without aluminium (AI) experiments have been performed in a stainless steel chamber of a volume of 1.5 cbm. These experiments were done under different ambient argon pressures up to 0.3 MPa. Gaseous reaction products were analyzed by mass spectrometry and chemilurninescence analysis. Solid reaction products were analyzed for measuring the carbon residue or unreacted Al It was found that the detonation products were highly dependent on the ambient pressure of argon. The most important changes of the reaction products and therefore also of the energy output were found between vacuum and atmospheric pressure of argon. With increasing pressure, H, and CO decrease and C02 , H20, CS, NH3 and CH4 increase together with the reaction enthalpy. By analyzing the physical structure of the carbon residue, diamonds have been observed between 4 and 7 nm diameter.