I believe it was Ruger that built a silenced revolver used the shroud that was previously mentioned. It was quite effective as a silenced weapon, but was quite a bit bulkier and a lot slower to reload.
A number of manufacturers have built silenced sem-autos with slide locks that prevent the slide from cycling, eliminating any possible residual pressure blast from the barrel and also eliminating the noise of the slide cycling and the casing being ejected.
A few days ago I found this illustration:
http://s124.photobucket.com/user/Sta...a/001.jpg.html
It shows the silencer that was used on the Model 1895 Nagant Gas Seal Revolver.