[neilep (OP)]

Dearest Academics Of Cosmopolitan Multi Specialist Expertise, []

Last night I saw the original Assault on Precinct 13 http://en.wikipedia.org/wiki/Assault_on_Precinct_13_%281976_film%29

Anyway, the baddies used silencers on their guns (I was going to say  'weapons ' instead of  ' guns ', but thought the ambiguity in the use of that word would make the deviant amongst you raise an eyebrow or two followed by a Kenneth Williams " ooooh Matron" http://en.wikipedia.org/wiki/Kenneth_Williams )

...anyway...and finally ..here is the question.

HOW do silencers silence the sound of the shot ?..I know they slow the bullet down somewhat and it would also be nice to know by how much ?



THANK YOU and hugs

[Heliotrope]

The suppressor as they're more properly called basically operates by allowing the escaping gas from the gun barrel a bit more space in which to expand.
So when it exits the muzzle it's not travelling as fast so the noise is lessened.
As the gas expands into the larger volume the pressure comes down so there's a bit less propelling the bullet so the projectile usually has a lessened velocity upon exiting the muzzle.

[ROBERT]

I know they slow the bullet down somewhat and it would also be nice to know by how much ?

How does a gun silencer work?
     
It is amazing that anything is able to silence a gun, but gun silencers actually work on a very simple principle.

Imagine a balloon. If you pop a balloon with a pin, it will make a loud noise. But if you were to untie the end of the balloon and let the air out slowly, you could pop it making very little noise. That is the basic idea behind a gun silencer.

To fire a bullet from a gun, gunpowder is ignited behind the bullet. The gunpowder creates a high-pressure pulse of hot gas. The pressure of the gas forces the bullet down the barrel of the gun. When the bullet exits the end of the barrel, it is like uncorking a bottle. The pressure behind the bullet is immense, however -- on the order of 3,000 pounds per square inch (psi) -- so the POP that the gun makes as it is uncorked is extremely loud.

A silencer screws on to the end of the barrel and has a huge volume compared to the barrel (20 or 30 times greater). With the silencer in place, the pressurized gas behind the bullet has a big space to expand into. So the pressure of the hot gas falls significantly. When the bullet finally exits through the hole in the silencer, the pressure being uncorked is much, much lower -- perhaps 60 psi. Therefore, the sound of the gun firing is much softer.

http://science.howstuffworks.com/question112.htm
 

[neilep (OP)]

The suppressor as they're more properly called basically operates by allowing the escaping gas from the gun barrel a bit more space in which to expand.
So when it exits the muzzle it's not travelling as fast so the noise is lessened.
As the gas expands into the larger volume the pressure comes down so there's a bit less propelling the bullet so the projectile usually has a lessened velocity upon exiting the muzzle.

THANK YOU HELIOTROPE !!

This is very fascinating and your contribution is appreciated .

[neilep (OP)]

I know they slow the bullet down somewhat and it would also be nice to know by how much ?

How does a gun silencer work?
     
It is amazing that anything is able to silence a gun, but gun silencers actually work on a very simple principle.

Imagine a balloon. If you pop a balloon with a pin, it will make a loud noise. But if you were to untie the end of the balloon and let the air out slowly, you could pop it making very little noise. That is the basic idea behind a gun silencer.

To fire a bullet from a gun, gunpowder is ignited behind the bullet. The gunpowder creates a high-pressure pulse of hot gas. The pressure of the gas forces the bullet down the barrel of the gun. When the bullet exits the end of the barrel, it is like uncorking a bottle. The pressure behind the bullet is immense, however -- on the order of 3,000 pounds per square inch (psi) -- so the POP that the gun makes as it is uncorked is extremely loud.

A silencer screws on to the end of the barrel and has a huge volume compared to the barrel (20 or 30 times greater). With the silencer in place, the pressurized gas behind the bullet has a big space to expand into. So the pressure of the hot gas falls significantly. When the bullet finally exits through the hole in the silencer, the pressure being uncorked is much, much lower -- perhaps 60 psi. Therefore, the sound of the gun firing is much softer.

http://science.howstuffworks.com/question112.htm
 

THANK YOU MR ROBERT SIR !!!....EXCELLENT STUFF !!!

[Karen W.]

 Very Interesting I did not know all that stuff!

[Soul Surfer]

The insde if a silencer is not empty it consists of a sequence of metal rings and cavities through which the bullet passes allowing the expanding gases to have a quick suggession of small expansions.

[lightarrow]

...that is, it's not very different from a motorbyke silencer...

[neilep (OP)]

Thank you for this additional info  Ian and Alberto.

I can see that the pressure drop is immense but how does that translate into a change of speed ?

[eric l]

Actually, the speed of the bullet increases as long as the pressure behind is higher than the (atmospheric) pressure in front.  [Well, that is of course if you leave friction in the barrel or the silencer out of the equation.] 
Generally speaking, a bullet from a long rifle will have a higher speed than a bullet from a similar cartridge, but fired with a pistol (or revolver).  Putting a silencer on a pistol does not slow down the bullet - or only slightly.