Since the beginning of the seventies TNO-Prins Maurits Laboratory (TNOPML) investigates the thermal stability of all stored land-force gunpropellants by isothermal microcalorimetry. The investigations are performed with IST (Isothermal Storage Test) at a temperature of 85 °C (358 K). Ammunition articles of the Dutch Ministry of Defense (MoD) are stored in temperature and humidity controlled bunkers of the Dutch army since the beginning of the nineties. However, the propellants kept at TNO-PML for surveillance purposes are stored in semi-closed glass bottles in a bunker with no climate control. To compare the influence of ageing of both storage environments, a microcalorimetric program with IST (Isothermal Storage Test, an in house developed technique at TNO) is carried out on the propellants of different selected munition articles. Among them are new and old articles as well as small and large caliber. A safe diameter of the propellants is calculated, which is characteristic for the self-ignition hazard. Furthermore, the heat production also gives an indication of the decrease of the calorific value for a storage period of 10 years in a moderate climate. The experimental results showed that corresponding propellants have comparable heat production in the IST. As a consequence, the maximum heat generation and the calculated safe diameter of a sample couple are in the same order of magnitude. It could be concluded that thermal stability of the samples is not significantly affected by the different storage conditions. Only when the munition article has no metal casing, some differences may occur.