They used dummy rounds that have the actual bullet, no powder, but real primers.
So close ups make the revolver look like its really loaded.
The gun was fired with just the primer which pushed the bullet into the barrel. When the replaced the dummy rounds with blanks and fired it, the charge was enough to fire the bullet in the barrel which struck and killed him.
If this movie was a western, its likey the same situation. That would explain the death but how do you wound the second person?
Fired all six or at least several until he saw both were hit , most likely.
Having him aim directly at the lens was amateurish it breaks the fourth wall … but like William Hurt that is the only work he can get anymore - top pay on a low budget shoot. And who would even want to see fat alec in a western??
Anything on the barrel could be a projectile, dirt, for example.
"how do you wound the second person?"