Since force is a parameter which is shape independent it is possible, and moreover advantageous, to use ground propellants for its experimental determination. These, due to their smaller grain size, give much shorter burning times than the unground propellants, which in turn reduces the pressure losses due to heat transfer to the containment vessel, and hence to a better agreement with theoretical values.
By using different grain sizes one can extrapolate to the force values at zero grain size and hence for zero burning time. These values are only on average about 2% less than the thermodynamically calculated values. Without extrapolation, as the present results show, one can expect a difference between the theoretical and experimental values of about 5%.
The conventional methods of determining force using closed vessels with volumes between 200 ml and 700 ml require a relatively large amount of sample material. The use of a ground powder allows the volume of the vessel to be reduced to 25 ml. This can be important when unknown foreign propellants have to be tested since these are usually only available in small quantities.