Three different gun propellants (A5020, JA-2 or L5460, NK1074) have been investigated up to 35years by mass loss at isothermal temperatures between 30 degrees C and 90 degrees C. From these data, activation energies for the different reactions of zero order (mass loss increase up to stabilizer consumption) and first order (solvent evaporation at begin) are derived. The mass loss data are described very well by a combination of these two reactions. Stabilizer consumption has been determined by HPLC. In case of diphenylamine (DPA), several consecutive products (mononitro-DPA up to tetranitro-DPA) have been regarded also. Activation energies are in the range of energies obtained by other methods: 84kJ/mol [A5020], 150kJ/mol [JA-2], 100kJ/mol [NK 1074]). Long term measurements show seasonal influence in the mass loss data. Respective graphs are shown in this work. At least four years of measurement are recommended to compensate for the signal drift caused by seasonal changes.