There were a few Revolvers specially made with zero cylinder gap and a simple maxim type silencer. These had to be so closely fitted that cylinder drag jammed them up after only a few shots.
Enough gas escaped that the shot wasn't truly silent, but muffled enough that you didn't get ruptured eardrums and there was no flash or dust kicked up in the shooters face.
I've only seen photos of one of these in what appeared to be a field trial.
I've experimented with custom fitting C&B Colt and .38 generic revolver cylinders for zero gap. Its not easy but the process is pretty straight forwards and greatly reduces flash at the gap, it noticably improved accuracy in each case.
Lathe turning the face of the cylinder is the first step, Its suprising hown many have dished chamber mouths.
By "zero gap" I mean no measurable gap using any commonly available shims. Less than .001