The collapse of any
individual wavefunction is random. The collapse of many is probabilistic. There is a tipping point that takes us from random events to non-random events. It is possible that the brain can influence the probabilities of many collapses, and possibly affect that tipping point. I have zero idea of the mechanism by which that happens and zero knowledge how or if free will comes into play there.
The other avenue for exploration is looking at complexity and chaos theory, although unlike quantum mechanics I don't know enough about it to speak on it. What I do know, is that a minute change in initial conditions (say a slight change at a quantum level) can cause completely different end states to occur. We don't really yet know if complex systems are deterministic.
Well that's the kicker. We don't know the mechanism by which the brain (conscious or subconscious) can make decisions. What I'm suggesting is that mechanism, and by extension free will, relies on the the probabilistic nature of quantum mechanics, but as I said I have zero idea how this mechanism occurs. I do believe in free will so I believe that this mechanism (or something similar, maybe taking into account complexity/chaos theory) exists, even if we don't know about it. Similar to how I believe that abiogenesis happened even though we don't have evidence of it yet.
As for your gun stand analogy that is not entirely true. I don't know whether this is relevant to the free will conversation but it is quite interesting all the same. Probabilistically, the scenario exists where the bullet goes through the target, or dosn't fire at all, due to the collapse of multiple wavefunctions in an improbabilistic way. An electron in the bullet can exist in two places at once. It could exist simultaneously inside and outside of the bullet. However, quantum rules don't just apply to subatomic objects. There is nothing to suggest that the bullet itself couldn't appear in two places at once, it would just require the incredibly unlikely event that the probability wavefunctions of all the particles in the bullet collapse in the same, incredibly unlikely way.
Classical mechanics, the world we know, is just an approximation of the world at a quantum level. The classical is an emergent property of quantum phenomena, it's the same set of rules. This guy explains it well:
Probability, quantum physics, and why (can't it/does it) apply to macroscale events? - Physics Stack Exchange
This is actually one of the things that needs to be grappled with when it comes to multiverse theory, if there is a multiverse, there should be a large number of multiverses where quantum effects are happening on a macro scale due to chance, but that's a different conversation.