I don't think taking MWI literally requires the assumption that every massive tunneling event is realized. Incredibly unlikely things might not be stable enough to form recognizable branches, the interference effects might be too strong before they fully split, or they might not contain something that can be considered a future version of one's self, so must be ignored.No. Or at least, if you're going to allow for that possibility, then you are allowing for possibilities that invalidate our belief in past data, and that version of the MWI undermines itself, as I argued in post #24. The chance that enough of the molecules will happen to all have tunneled into the "can't fire" state, and none of them will have tunneled back into the "can fire" state, at the exact instant that you try to fire the bullet, is comparable to the chance that @DrChinese actually was president of the US 5 minutes ago, but then a quantum fluctuation happened that changed everything on Earth, including all of our memories, to the state we all perceive and remember now. And if you allow for possibilities like that, all bets are off and there's no point in doing science at all.
Looking at it backwards is also helpful. Maybe there is a very small contribution to my current state from almost-orthogonal past states where Dr. Chinese was president. But that past state is so incompatible with my current personal state (containing my memories) the contribution will be too small to notice.
I'm not suggesting these are solved problems, because I suspect one needs to really understand how people perceive the world and form their sense of self to fully connect objective unitary evolution to the subjective experience of life inside that universe.