The depiction of guns in movies is, famously, not very exact. (Guns are cocked dramatically a thousand times over and safety standards don't even seem to exist).
However, one aspect I was wondering about is the (in)famous silencer: Transforming a loud -bang- into a small "pew pew". (For examples, check the first scene from "Sin City", where the narrator even comments on the gun being turned into "a whisper" by the silencer). This would mean that a gunshot gets reduced from about 150 to 170 dB to around 20 to 40 dB. Now this, in movies, is always achieved by a simple metal tube screwed on top of the gun.
Now, as someone who does not live in the US and doesn't know a thing about guns, I was wondering: Can a gun be silenced to a level of about 40dB?