This is what I was thinking. If it was a SAA then that means the actor (Baldwin) would have had to deliberately cock and fire the pistol. Which means about the only way this was an accident is if the scene called for firing the gun at the camera. Were they shooting or rehearsing a scene? If not then Baldwin has a lot of splaining to do. If this was truly an accident, and it likely was, I still feel sorry for him.
In the case if a bad sear, the gun might go off if only cocked. That might be why there were complaints about the gun earlier.