The importance of filling grade in the sample container as well as the moisture content of the sample at heat flow calorimeter analyses of nitrocellulose propellants is studied. The differences in heat production rate and total amount of energy released are small between samples of different filling grade but the differences increase with increasing analysis temperature. The filling grade has also shown to be more important at analyses of double base propellants than for analyses of single base propellants. Since the importance of filling grade is more pronounced for the level of the initial heat production rate than for the remaining of the analysis it is recommended that the limits based on the level of initial heat production rate that are used for heat flow calorimetry analyses at present are supplemented by a limit for the total amount of energy released. An increased moisture content of the propellant sample results in a markedly increased heat production rate of all propellant lots analysed. To avoid exaggerating or underestimating the risks at continued storage of propellant lots it is proposed that the samples are conditioned at a specified relative humidity before the analyses. Further studies of how such a conditioning of the samples best can be carried out are required.