Well, I was watching so many action movies but every time I see a gun with a silencer I can't stop wondering how it works. As usual I checked on the net and Bingo! I got the answer. But the answer was amazingly simple. There is absolutely no mechanism in a silencer.
All that's required is that, the silencer should be slightly bigger than the gun barrel. That's all it takes to mute the firing sound (not exactly mute though). Well, I'll use the same example as I got through.
Imagine a balloon filled with air. You pop it with a pin and it burst making a huge sound. That is because the air pressure inside the balloon is very high and when the balloon pops, there is a huge drop in the pressure in a very quick time, creating the sound. But when you remove the end of the balloon, the air pressure reduces slowly and hence the sound is very less.
Similarly, in a gun, the gun powder is ignited behind the bullet. The gun powder produces a high pressure pulse of hot air. And as the bullet is out of the barrel, so is the air behind it. The air pressure in the barrel is around 3000 pounds per square inch (psi). So you hear the sound as there is a huge drop in the pressure. But in case of a silencer, when the bullet is out of the barrel, the air is released into a slightly larger volume and hence there is no huge drop of pressure but a considerable one. When the bullet is out of the silencer, the pressure is only 60 psi. Hence the firing sound is so much reduced.
Simple, yet effective!