High-explosive separators used to separate structures in space systems and launch vehicles have many advantages, including low cost, high reliability, and high operating energy. However, there are also critical disadvantages such as a large pyroshock and the potential for debris. Low-shock separation devices address these disadvantages. The pressure-cartridge-type device, covered in this study, is attractive because of its high load capacity and high reliability. Its separation behavior, however, is complicated and not understood well because the separation happens within a few milliseconds through complex mechanical interaction. In this Paper, a mathematical model is established to predict the separation behavior of a ball-type separation bolt. The model consists of simultaneous differential equations that include a combustion model and equations of motion involving interactions between various components. Using the model, the effects of two representative design parameters, the coefficient of friction and amount of propellant, were investigated. A suitable range for the coefficient of friction was identified, and the amount of propellant was shown to be a function of the acceptable shock level and the safety factor for separation. This study showed that the complex performances of the separation bolt can be assessed with a straightforward, computationally efficient model.