Multi-dimensional multi-component two-phase flow modeling of solid propellant combustion in weapons is the new trend of the interior ballistics codes. Most of these codes are designated to large caliber guns and rockets simulation. Only a small number of investigations on small-caliber gun have been recently reported, where the need of high-performance and reliable small-caliber guns stimulated significant interest in developing techniques to understand the phenomenology of small-caliber ballistics and predict the behavior and the performance of this type of weapons. In this paper, a numerical model describing the combustion of solid propellant in small-caliber gun is presented. The governing equations with customize parameters were derived in the form of coupled, non-linear axisymmetric partial differential equations. They were further implemented into the CFD code Fluent. A numerical test showed that Fluent is able to handle correctly the interaction between the moving projectile and the combustion gases in the chamber. The interior ballistics curves along with the performance of small-caliber gun 5.56 mm were adequately predicted. The numerical results were in agreement with the experimental results.