Accelerated Ageing of Pyrotechnics: 16mm Signal Cartridge - White

The 16mm Signal Cartridge White is used by all three of the UK services. The explosive components are a rimfire cap, a propelling charge of sulphur free gunpowder (SFG), a priming composition based on silicon, potassium nitrate and sulphurless mealed gunpowder, and the main pyrotechnic composition which contains magnesium, barium and strontium nitrates, a colour enhancer and a binder.Cartridges from two different lots were subjected to diurnal temperature cycling for periods of up to 50 weeks. At intervals of 10 weeks, six cartridges were removed from the ageing trial and subjected to critical examination.Quantitative chemical analysis of the main pyrotechnic composition was undertaken, free and total magnesium determinations were made and the heat of reaction was measured using an adiabatic bomb calorimeter.The SFG was subjected to microscopic examination to assess possible caking and/or leaching of the potassium nitrate. The temperature of ignition of the three pyrotechnic compositions was measured by differential thermal analysis.Additionally, the cap was subjected to fire/no fire testing.The performance of the cartridges was determined by proof fire testing which included measurement of the burning time and the heights attained on firing. Other stores enabled the burning time and light output of the main composition to be determined.The results of these tests are reported and discussed in detail, and recommendations for the safe in-service life of this signal cartridge are made.