Revolvers cannot be effectively suppressed because gas escapes from between the cylinder and the barrel creating noise (there are some exceptions). The big shell that encloses the cylinder of the PSDR 3 prevents the gas from escaping. This combined with a big suppressor and a subsonic .45 ACP round causes a noise reduction from 136 dB to 90 dB which is comparable to a CO2 air gun. Decibels are a logarithmic unit of measurement, so a 46 dB reduction is significant. In theory this gun should make a lot less noise than a suppressed semi-automatic pistol because there no slide slamming open and closed.
— S&W 625 fully suppressed revolver | The Firearm Blog
I’ve always been under the impression that it was impossible to silence a revolver, and really, why would you go to the trouble? What possible benefit would you have?