The manufacturing process of a pyrotechnic device containing compressed powder has been investigated with the purpose of improving process consistency and product robustness. Aspects of the manufacturing process have been modelled, in particular the powder compaction process, the container assembly and the "leak check" test. The mechanics of powder compaction have been considered and the relevant powders have been characterised and represented using the modified Drucker-Prager constitutive model. Simplifying assumptions that have been made in defining the powder properties in terms of the available experimental data are indicated. The processes of pre-compaction and attachment of the cup to the header in the sub-assembly machine followed by the leak check test have been simulated using finite element analysis (FEA). The modelling activity in conjunction with experimental and product observations have highlighted the irreversible changes in powder density distribution following each of the stages of the process and the effect of these on the final product. The investigation provides an example of the application of FEA in solving a practical problem involving powder compaction.