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how is a sonic boom created

im trying

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Actually, the sonic boom sound a supersonic bullet makes is kind of a high-pitched cracking noise, like a really dense twig snapping under pressure. The big loud boom a gun makes is all those expanding gases that come out the barrel colliding with air that can't get out of the way fast enough. That's why a silencer on the end of the barrel works, and why it doesn't silence the crack of the mini sonic boom the bullet makes (although it does muffle the boom of the gases, which are also traveling supersonically). 

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Combination of very hot expanding gases exiting the rifle barrel very quickly.  Certainly exceeding the sound barrier which at sea level is about 1050 fps.  Kinda.  Most all rifle bullets exit the barrel in speeds much greater than that.  The gases actually somewhat exit BEFORE the bullet does.  Windage.  Gases getting around the bullet.  But usually just a little bit.

Because the exiting gases are traveling much faster than the speed of sound, the air around the muzzle gets quickly compressed.  This creates shock waves.  The shock waves of the expanding gases creates the sonic boom.  That shock wave quickly down speeds to sub sonic sound waves.  BOOM!.  The down range CRACK is caused by a super sonic bullet.

Cans, (suppressors) work by slowing down, expanding and cooling off, (somewhat) the gun powder gases while still inside the suppressor.  This gets converted into heat.  The cooled expanded and slowed down exhaust gases exit the can more slowly.  This quiets down the gun report.  Sub sonic bullets work best with cans.  Cans must be well made.

High power rifle suppressors are heavily built with thick steel.  Some use titanium which erodes quickly. Some suppressors used water as a sound moderator.  They are called wet cans designed to be used in sea water.  The can gets shaken ed out and the residual remaining water gets turned to steam, helping the sound suppression for the first shots. 

In places in Europe suppressors are legally REQUIRED.  Too many people.  In the USA suppressors are heavily and legally regulated by the BATFE.  Bureau of Alcohol Tobacco Firearms and Explosives.  Legal suppressors are no more than mufflers for guns.  But in the USA one must go through a heavy legal process before that tax stamp, (license) is issued.

All Oregon State, US Code Laws, (USA) and NFA Rules Apply.  NFA is the National Firearms Act.  I was told to say this when I talk about machine guns and suppressors as a legal declaration that with proper licensing machine guns and suppressors are legal to own and use in the State Of Oregon USA.  You firearm and suppressors laws may vary greatly.

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10 minutes ago, im trying said:

I thought it was because they broke the sound bearer 

Most rifles and some handguns fire bullets that do (1100+ feet per second is usually a supersonic round), but bullets are small compared to aircraft. A big fighter jet breaking the sound barrier is creating big shock waves, and thus a big sonic boom is heard. A little bullet goes *crack!* because its shock waves are little.

A shotgun fires a bunch of even smaller pellets, which are normally subsonic (don't break the sound barrier). It still makes a big *boom* though, even louder than the rifle or handgun. That's the rapidly expanding gases meeting the air that can't compress or get out of the way fast enough.

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When an object moves through the air, it compresses the air molecules ahead of it. These pressure pulses ( essentially a sound wave ) are able to move forward at the speed of sound, and impact other molecules to move them out of the way.
When an object is moving supersonically, the compressed molecules are no longer able to travel ahead and move subsequent molecules out of the way. The pressure pulse 'piles up' ahead of the moving object and creates a shock wave. This shock wave is in the shape of a boat's wake, except its conical, and the faster the speed ( supersonic ), the more acute the angle of the 'V', or cone. All along this 'V' there is a steep pressure gradient, which get weaker the farther away you are along the 'legs' of the 'V'.

A large object, like an F-111 aircraft, which can fly supersonically ( M 1.2 ) at 200 ft altitude, would cause considerable damage/injuries if flown over a city.

It is said that if the squadron of F-111, which attacked Lybia in the 80s, hadn't dropped any bombs, but had just flown supersonic over the target, they could have caused more destruction than the precision guided bombs, and possibly have taken out Muammar Gaddafi.

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