When Frank spins the open cylinder of his double-action revolver, we hear a clicking sound. In reality, the cylinder on such a revolver spins unimpeded and makes almost no noise when rotated in the open position. Clicking cylinders are unique to single-action revolvers.
Chris tells Frank that the .22-caliber revolver Frank will use for an assassination doesn't require a silencer, apparently in the belief that such a pistol is inherently quiet. But a .22 revolver emits a noticeable report; if noise suppression was a concern, the gun should have been equipped with a silencer.