In this paper, we propose a new twin-barrel gun model for calculating firing on the elastic ground to study the effects of structural parameters on the weapon's performance. This paper intends to provide a theoretical basis and establish a specific model of twin-barrel gun, to build a system of differential equations of vibration, and to determine the rules of vibration of the gun when firing on the elastic ground. The method is used to establish a model of two sets of automatic firing systems by dynamics of a multi-body system. The results of the calculation revealed the instructional significance for improving the vibration performance and increasing the firing accuracy. Experiments were tested out on a 37 mm twin anti-aircraft gun, type 65. The results of the theoretical mathematic model provide a good correlation to experimental data. The maximum amplitude deviation on the horizontal plane does not exceed 8.1%, while in the vertical plane does not exceed 6.4%. The outputs can be used for validation of a dynamic model of a weapon system while firing on the elastic ground, and the procedure can be used as an example of a practical technique and methodology for other weapon systems.