Integral Rocket Ramjet (IRR) type propulsion systems have many advantages over conventional solid rocket motors when used in tactical missile systems. Nozzleless boosters are one of the applicable concept choices for the system. The present approach includes performance prediction of nozzleless solid propellant rocket motors (SPRM). Quasi one dimensional internal ballistics model is constructed and solved numerically through inside the motor. To predict the burning rate, universal erosive burning rate relation developed by Mukunda and Paul  is used. The results of the numerical internal ballistics simulations are compared with the experimental nozzleless motor firing results found in literature. It has been demonstrated that numerical results are in good agreement with the experimental data in terms of chamber pressure and thrust.