Projectile’ penetration into the target is a complicated mechanical process that has been under consideration by researchers due to its military and non-military applications. The military applications include the design of structures that are resistant against projectile’s penetration, anti bullet armors, design of light armor systems (personal armors) for the protection of police officers, governmental authorities and martial individuals, missiles and non-military application like production of machines for traortation of dangerous materials, strengthening the body of helicopters and aircrafts, design of navies’ body, protection of space crafts, securing of head centers, design of protective coverings against rays of nuclear reactors and etc. In the above mentioned applications the impact loads due to external reasons like impact of the missiles or rackets or internal reasons like the increase in imposed pressure applied to these structures are of the most important applications of this subject.The study of impact and penetration phenomenon is too intricate and includes many problems to deal with because it involves different parameters. Some of these parameters are: propagation of elastic and plastic waves, mass and heat transfer, work hardening, friction, hydrodynamic flow, different fracture mode, the effect of geometry of impacting materials, resistance and the density of impacting materials and other parameters. In the recent fifty years many scientist have worked in this field. They have studied this complicated phenomenon with different analytical and experimental methods together with perfuming numerical simulations. Therefore the importance of this subject causes this project to survey the penetration process both experimentally and numerically.In this thesis, the penetration of a projectile with noise hemispherical into the targets with three adjacent layers (without air gap) with different arrangement and materials is been studied. The targets are circular plates with the diameter of 240mm and the material chosen is copper (ofhc) and AL1100 and the material of projectile itself is silver steel . For implementing the experiments a single step gas gun is used. The targets are arranged in three layers and without air gap. . While defining ballistic limit for the projectile-target system, the effect of layers arrangement sequence and material in their ballistic operation is pursued. The result of the experiments showed that (among eight possible different arrangement) if the aluminum and copper be arranged in sequence that the aluminum plates (harder material) are placed in the two first layers and CU (softer material) is placed in the third layer, the resistance against penetration will have the maximum value. Key Words: Penetration, Projectile, Gas gun, Ballistic limit velocity, Aluminium, Copper