How does a gun silencer actually works

A silencer, also called a suppressor, is a cylindrical device that fits onto the end of a gun barrel to dampen the sound and flash as ammunition is being fired. Silencers were invented in the early 1900s and largely made commercially viable by inventor Hiram Maxim, who is also credited with creating the automobile muffler around the same time. Both use the same actions in reducing the sound of explosions, whether it is from a gun, or the controlled explosions of an internal combustion engine. 

The cause of most of the noise from a gunshot is due to what is called the muzzle blast. Bullets work by creating a small explosion. The explosion creates pressure inside the gun, forcing the shot out of the barrel at extremely fast speeds. When the pressure is released from the barrel it creates a noise in much the same way as the pop of a cork removed from a bottle of champagne. The silencer is made of a machined metal cylinder. Inside the cylinder are 4 to 15 compartments, called expansion chambers, separated by walls called baffles. The baffles direct the pressure of the gases from the explosion into the expansion chambers. The chambers create a volume of space up to 30 times greater than that of the barrel for the gases to escape. Since the gases are allowed to expand in the silencer, the difference in the change of pressure is not as great, so it creates much less of a sound. Since the pressure is not as great when being released, the silencer also slows the bullet. This can reduce the sound by slowing supersonic bullets to sub-sonic speeds. This means the bullet no longer creates a sonic boom as it travels through the air.