In the present research, an experimental and numerical investigation has been performed to study initial pressure rise in multi grain solid rocket motor. A cluster of seven uninhibited tubular grains of double base propellant is analysed to get near neutral pressure in rocket motor. It is experimentally observed that in some static firings initial pressure rise in first 100 ms is higher than the predicted value of similar to 7.5 MPa. The average pressure in the rocket motor is similar to 7 MPa and total burning time of these grains is similar to 2 s. ANSYS software is used for numerical analysis to investigate the effects of various % openings of nozzle end (NE) metal grid on pressure rise in the rocket motor with and without peripheral opening. The analysed results are compared with experiments. It is found that, as the %opening of NE metal grid increases, the initial pressure in the rocket motor decreases. The peripheral opening is also important to reduce pressure rise in rocket motor. This study helps in reducing the initial pressure rise in the combustion chamber which is essential for safe working of the rocket motor.