Powder injection molding (PIM) is capable of manufacturing complex small components out of metals and ceramics. With increasing market demand micropowder injection molding (micro-PIM) is improving rapidly which calls for improved numerical models of different stages of PIM. The injection stage is quite important as different defects may occur during injection that cannot be eliminated in the subsequent processes. Injection pressure and velocity are critical controlling parameters to manufacture a defect-free component. However, in most of the simulations, either injection pressure or injection velocity is taken as a constant value, while in reality, the injection molding of the piston moves at different speeds, and injection pressure and velocity change accordingly. In the experimental part of the present work, the piston movement is tracked using a high-speed camera which was mimicked in mold filling simulation of an alumina feedstock, considering the Dynamic Mesh approach. The solution of the full Navier–Stokes equation in an Eulerian-multiphase framework is used to simulate the mold filling where the secondary phase is air that is displaced by moving melt front. Additionally, a scalar equation was used to account for the liquid fraction of the feedstock. It is further demonstrated that the proposed model provides insight into the fluid-dynamic aspect of the mold-filling process.