Putting the revolver in single action can lead to a negligent discharge with tragic results.  One of the most infamous examples was the case of New York vs. Frank Magliato.

Mr. Magliato was a licensed NYC gun owner with a Colt Detective Special.  He was attacked twice in one day by an armed junkie. During the second attack Mr. Magliato cocked his revolver while trying to defend himself and it discharged unintentionally killing the junkie.  Mr. Magliato’s trial hinged upon several of his pre-shooting decisions. Of critical import was his decision to cock the revolver. Mr. Magliato believed that cocking the revolver rather than deliberately pulling the trigger set the stage for a negligent discharge. That shot (the negligent discharge) that should have been by all reasonable self-defense standards an intentional discharge was used against him as an example of his overall reckless behavior. Subsequently, Mr. Magliato was initially convicted of murder and then later reduced to manslaughter; Mr. Magliato served several years in New York’s Fishkill State Penitentiary for cocking his self-defense weapon rather than pulling the trigger straight through.  For a more detailed overview of this event you can check out two competing versions. The first you can find on -line from Massad Ayoob’s The Ayoob Files and the second from the book The Professor and the Prostitute by Linda Wolfe. The section on the Magliato shooting will be listed in the chapter titled Dented Pride