On my last forensic post, one of the commenters wanted more information about silencers. So, here it is:
Why do guns make so much noise?
1) When ignited, gunpowder produces a huge amount of rapidly expanding gases. These expanding gases propel the bullet out of the gun. The loud bang noise is created when the bullet is forced out of the end of the barrel at high speed.
2) The second is the supersonic crack of the bullet. It is not possible to reduce the sound level of a supersonic bullet. For a sound moderator to be really effective, it must be used with ammunition whose projectiles travel at less than the speed of sound.
What are suppressors (silencers)?
A silencer is typically made up of a long steel cylinder. The cylinder will be much wider in diameter than that of the caliber of gun that the particular silencer is designed for.
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The second section consists of a series of metal baffles, with a central hole to allow the passage of the bullet. The function of the baffles is to progressively deflect and slow the flow of gas emerging from the expansion chamber, so that by the time the gases emerge from the silencer, their flow is cooler, at low velocity and silenced.
What can you do to silence a gun completely?
Because two things make a boom noise when you fire a gun, two things need to be silenced.
1) The pressure of gas- if you only silence the pressure of the gas, you will still here a loud sound because the bullet is supersonic - likely to produce a muffled crack, or to sound like a car door being slammed.
2) The second is a sonic boom as the bullet breaks the sound barrier. To silence this bang, you need to use subsonic bullets or ammunition.
What home-made silencers work?
1) A plastic soft drinks bottle can be made into a fairly efficient silencer that will work for a limited number of shots before it breaks up.
2) Wet silencers (not really home-made) but you can find more info here.
What home-made silencers DON'T work?
1) Potatoes at the end of the barrel definitely don't work - unless your plan was to shoot a potato.
2) The pillow doesn't really help, either, though it does have the benefit of minimizing or negating blood splatter during the shooting.
3) In the 2007 film Shooter, a silencer was made out of a can filled with socks. It would have been better if the socks had been left out, since all they would do was take up space that the gas could have expanded into. 4) Most packing materials are useless.
Some really good YouTube videos showing silencers (suppressors) in action. In the second video, the man is using a suppressor however, he is not using subsonic bullets.
Sources: ehow, io9.com, http://www.swrmfg.com/, newsoftpedia.com
Picture source: here