Mosin Nagant revolvers were design in such a way that the cylinder pushed against the barrel to seal the gasses making a suppressor work with a revolver.
I doubt that anyone on Hollywood is aware of that.............
It would also have to be sealed at the rear of the cylinder, where the hammer or firing pin strikes the cartridge to ignite it, in order to get effective silencing—there are two gaps, the cylinder gap you refer to and the one I mention, that are significant for sound, smoke, gas, heat, fire, gunshot residue, etc. escaping from the revolver cylinder during firing.