In order to investigate the physics behind the dispersion and test future design changes, a detailed finite element model of the PHALANX gun was developed. This is the first finite element model of the gun ever. The normal modes of a single barrel have been matched favorably with those of a real barrel. This model has been used to calculate the normal modes of vibration of the whole gun in order to predict the motion of the complex system. Barrel tip displacement, which plays a critical role in the dispersion pattern, was determined after applying the periodic firing excitation force and damping. Its motion corresponds well to the 2 mradian dispersion. In addition, its first mode of vibration at 14 Hz appears to be significant in the analysis of the dispersion data. This analysis has focused attention on certain components of the gun, such as the double angular contact bearing, which may be a leading cause of the dispersion pattern. Finally, this gun model can also support design changes such as the addition of barrel restraints or the proposed new barrels and their effect on dispersion predicted prior to any actual hardware tests or procurement orders.