The principle of working of a car muffler and a suppressor (silencer) are the same. There are three stages in a silencer that have to be incorporated. The heat is absorbed and dissipated rapidly in the first stage of the silencer. Gases are also cooled quickly and hence there is a reduction in the compression. In the second stage the bullet speed is reduced to sub sonic speeds with the help of plastic or rubber washers. In this stage also compression is reduced. The most complicated stage is the third stage that has wooden washers and rubber discs. The rubber discs are placed between wooden washers. Rubber cylinders are used at the end of this stage to slow down the air that goes out. All these stages have to be incorporated within a 1 �” PVC pipe. The PVC pipe should be of type 300 PSI. You can refer to some websites that give the exact specifications and dimensions of the materials that are used in the three stages of the silencer.