How I feel the shooting happened
Keeping in mind I am not an Alec Baldwin fan --- he was pretty good when he started out and getting better than he decided to give up acting and become a STAR,, I happens
With a Colt SAA, There are 2 positions for the Hammer, 1/2 cock for loading, and unloading,FULL cock for fireing
AT the 1/2 cock position it is hard to pull the trigger, so you don't shoot yourself while loading
SOO you get the gun loaded, Hammer down---- Nowadays that's safe, BUT the old timers used to put the hammer down on an empty chamber, would matter in this case
OK so hammer down and you're smart-ass Alec fucking around with the gun, He pulls the hammer back, NOT far enough to engage the safety notch at 1/2 way, but close, and the hammers slips out of his thumb,
THERE IS enough tension on the spring to fire the weapon
This is likely what happened