Greetings in that Divine and Most Precious Name of Our Lord and Savior Jesus Christ!
In this scenario I would say that the interaction of free-will only is in consequence to the firing of the gun itself. God alone controls life and death, some folks survive horrifying injury, others die peacefully in their sleep. God allows our free-will to interact within His Creation, however, in regards to larger matters of life and death we can suppose that the Omnipotence of God trumps the powerful gift of human free will. Humans can chose to shoot the gun, but only God can decide whether or not to take the life of the shooting victim.
Personally, I conceive of human free-will being similar to the way we physically operate within gravity or other fundamental cosmological forces. God has predesigned all the parameters of the Cosmos, just as a programmer designs all of the environs of a video game or a simulator, and we have the entire free-will to interact within any of the variables or parameters of God's Creation, however as Creator and Sustainer, God is perpetually in full control and yet also grants perfect free-will. We can chose any of our options, just as in the three dimensional world we can move our hands up or down, left or right, and yet the fundamental forces such as gravity are always present interacting with our decisions. We only are free to make choices grounded in the reality of the interaction of the forces, just as we are only free to make the decisions within the opportunities that God provides.
So in this example, the free-will was to shoot or not to shoot, to duck or not to duck, to have been at the wrong place at the wrong time or to have been in the right place, several converging factors determine the outcome, but the overall conclusion is on God.