In many solidification processes, particularly in the presence of grain refiner, solid grains initially form as free floating particles suspended within the liquid metal. As these grains continue to grow in number and size, their interactions cause them to form a permeable rigid solid structure. The majority of these models for equiaxed solidification assume that the transition from a slurry of particles to a rigid solid structure occurs at a fixed, uniform solid fraction. This approach does not include the influence of the local velocity field on the likelihood of packing. The present study investigates the effects of three different methods of including the solid particle velocity into packing rules and applies them to simulations of static castings. The advantages and disadvantages of these approaches are discussed in relation to the more common constant packing fraction model.