Traditional single-action revolvers were carried with an empty chamber under the hammer due to the possibility of dropping the gun on the hammer and getting that loud, unwelcome noise. This possibility also existed with S&W DA revolvers until 1943, when a sailor dropped an M&P on the hammer and the discharge killed another sailor. S&W designed the current hammer block to take care of that.
Ruger Blackhawks were re-designed in '73(?) to incorporate a hammer block so the gun could be carried with six rounds loaded, and this was a selling point in their marketing. My OMSBH was made in '67 and I carry it with an empty chamber under the hammer.