[tlb]

For this to work, the gun has to terminate your consciousness before the state of the coin can become entangled with the world. Objects as large as guns cannot (currently) be kept in an unentangled state for the milliseconds required for a bullet to do its work. If it were possible, the entire gun-bullet-head system would need to be cooled to microkelvin temperatures, at which guns or consciousness don't work.

[nessus42]

I don't understand your comment. In the Everett Interpretation, the wave function never collapses. Everything is always entangled. "Decoherence", however, causes the perception that the wave function collapses, and consequently this interpretation is often called the "Many World Interpretation", because the theory results in a different "world" (for all intents and purposes) for every possible outcome.

Hence, in the Everett Interpretation, if you shoot yourself using such a quantum gun, every time you pull the trigger, there will end up being one "world" in which the gun didn't go off and one world in which you put a bullet in your head.