An attempt is made to model the design of grain selection during single-crystal solidification of an Ni-based superalloy by the Bridgman method. Various geometrical designs of the starter block and spiral grain selector are chosen and their effects on crystal orientation of the single-crystal part are studied. The competitive grain selection is simulated utilizing the cellular automaton finite element module of the ProCAST software. The simulated results are validated against the experimental observation of grain structure along with the crystal orientation measured by the electron backscatter diffraction (EBSD) and rotational orientation X-ray diffraction (RO-XRD) techniques. The results show that in order to obtain the single crystal with a minimum deviation from longitudinal axis, the height and diameter of the starter block as well as the height and the take-off angle of the spiral should be optimized. It is found that the diameter/height ratio of the starter block should be less than 0.6 to obtain a well-oriented single crystal prior to entrance of solidification front into the spiral. The height of starter block is found to be more influential than its diameter in selecting the suitable single grain.