I'm saying 90-100 decibels
That's about right. 75-80 is possible with the right configuration. The quietest gun I can think of is an integrally suppressed bolt action pistol chambered in subsonic 9mm: the B&T VP9. It's essentially a modern Welrod. Like all B&T firearms, it's prohibitively expensive and that one was very limited in production with only 250 sold.
Edit: I am wrong. Even that pistol is still 125dB with subsonic loading. From B&T's website
This produces a noise level as low as 129dB when using standard 124 grain NATO ammunition. This sound reduction can be further decreased as much as 4dB by using subsonic ammunition. This noise is about the same as a car door closing.
Suppressed .300 blackout is the quietest centerfire round at around 80dbs.
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