I bet Baldwin told his teacher that the dog ate his homework.

The real issue is: what was live ammo doing on a movie set? It's the absolute last place to have live ammo. I wonder if someone deliberately placed it in the gun to sabotage the movie.

As for the gun: It would be crazy for them to use an authentic, cowboy-era single-action revolver with no transfer bar in a movie. Those guns are collector items that could be damaged or destroyed by modern ammo. Excellent looking, non-firing replicas are available everywhere; the special effects crew could have added flash and noise in "post production." And, all anyone had to do (and should have done) to check the gun was to look (with the hammer down) at the front of the cylinder to see if the rounds were capped with bullets or were crimped to indicate blanks.