Silencers are illegal devices that criminals use to make their guns silent.
Don’t believe that!
The sound of a gunshot registers anywhere between 140 and 160 decibels. Silencers are real, and they do reduce the volume of a gunshot – to about 120 decibels. That’s still louder than a chainsaw from three feet away. A lot louder.
Silencers, also known as suppressors, are basically metal cans that redirect the escaping gas from a gunshot through a series of internal chambers, reducing its velocity. The silencer was invented in the early 20th century and was so popular in the 1920s and 30s that they were sold through sporting goods magazines and in hardware stores.
Later designs attempted to shift the frequency of the gunshot sound into the ultrasonic range, making it inaudible to humans (but presumably very annoying to dogs). In practice, this is nearly impossible to achieve since the sound covers so many different frequencies.
Silencers not only do little to reduce the sound of the discharged round, they do nothing at all to reduce other sounds created by firing the weapon. These can include the small sonic boom produced by the bullet as it breaks the sound barrier, the ejection of the fired cartridge case and loading of the next round.
Since silencers have legitimate non-criminal uses (reducing the possibility of hearing damage), they are legal to purchase in 39 of 50 U.S. states. Federal law does provide for severe minimum sentencing requirements if a crime is committed with a silencer-equipped firearm.
Bonus Fact: the inventor of the silencer also invented the automobile muffler, using a similar design.