Dado'3, it was his bullet, he is responsible for it. What happened to the brave TFL talk about perps "taking responsibility"? He cannot step on the brakes once the bullet is launched.
The woman did not jump in front of his pistol at the range. He, and he alone, had the ability not to fire. If someone jumps out in front of your vehicle on the interstate, you may or may not be able to swerve or brake, you can always not press the trigger or, better yet, leave it in your holster.
YMMV and we may see what comparative fault a civil (or criminal) jury concludes.
"Arguments of policy must give way to a constitutional command." Payton v. New York, 445 U.S. 573, 602 (1980).