Testing of two M7 propellant lots in closed vessel

Two different lots of M7 propellant for use in M72 rockets have been tested at room temperature in closed vessel to investigate if they have different burning properties. The studied lots were lot NARA 128 and lot NARA 188. The firings were performed in a 700 cm3 closed vessel. Tested loading densities were 0.10, 0.15, 0.20 and 0.233 g/cm3 for each of the lots. The obtained pressure time curves for the two lots with the same loading density were compared, and for three of the loading densities the pressure rise was significantly slower for lot NARA 188 than for lot NARA 128. For the fourth loading densities no big differences in the pressure time curves were observed. Obtained impetus was slightly higher for lot NARA 188 than lot NARA128. However, the obtained difference in impetus is within the accuracy of the test method. The obtained burn rate for M7 lot NARA 128 propellant in the pressure range up to 1/3 of maximum pressure is higher than for lot NARA 188. In the pressure range from 1/3 of maximum pressure the burn rate goes from equal to being higher at maximum pressure for lot NARA 188 than for lot NARA128. A comparison of obtained burn rates of lot NARA 128 and lot NARA 188 with earlier tested M7 propellant shows that lot NARA 188 is the lot that differs from the normal properties of this type of propellant.