Time to clean up the messy reporting on Alec Baldwin’s negligent shooting of cinematographer Halyna Hutchins and director Joel Souza. We still do not know what firearm was used, but the film was being shot on a movie set used principally for 19th Century westerns–Blazing Saddles and Jimmy Stewarts’ The Man From Laramie. So it is highly likely that Baldwin was shooting a revolver and not a semi-automatic pistol (e.g., Glock, Sig Sauer, Berretta).
Semi-automatic pistols are a 20th Century invention and became a staple of military equipment after World War II. There are two types of revolvers–Single Action and Double Action. Single Action means that when you pull the trigger the hammer is released and the gun fires. This was in widespread use in the West during the cowboy era. The cylinder that holds the ammunition is not easily removed and you must open a loading gate to insert only one round at a time into the revolver. Double Action is what most people associate with a revolver. That means when you pull the trigger it cocks the hammer and then, as you continue to apply pressure to the trigger, releases the hammer and fires the pistol.
There also is no such thing as an “accidental” discharge. If a firearm is fired unintentionally it is negligence. Gun accidents are caused by only two things–ignorance and/or carelessness. If you are holding a pistol, it will not fire unless you put your finger on the trigger.