A sound moderator will not suppress most revolvers to much extent due to the gap between the cylinder and the barrel. Whilst it will reduce muzzle noise, the additional back pressure may well increase the noise from the gap,
This noise is the sonic bang due to the velocity of the bullet.
A sound moderator fitted to a .22 revolver used in conjunction with sub-sonic ammunition will definitely reduce the noise. The bullet is travelling at sub-sonic speed therefore no sonic bang.
The only revolver which will definitely work with a sound moderator is the old Russian Model 1895 Nagant. It used special ammunition and a cylinder that moved forward to seal the gap.
Advice is definitely do not attempt to put a silencer on a centre fire revolver. Not only will it make the gun enormous, the moderator will not effectively reduce the sound. Moreover, threading most revolver barrels is not straightforward, and if done externally will usually mean that the fore sight must be sacrificed. Threading internally will overcome this but is even more complicated. This also precludes the fitting of standard moderators that have a ½" UNF female thread for attachment.
The only handguns that can be effectively sound moderated are those of the single shot sealed breach type, chambered for sub-sonic ammunition.