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That means that in the entire flight of the bullet, there will be less than one rain drop in it's entire path

Now that is good statistical analysis!
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There's essentially 1 drop of water SOMEWHERE in the flight path of every 10th bullet.

From how I read your math on getting the original raindrop chance I think you calculate the chance a raindrop would be entirely in the same spot as the bullet at any point in that 2 seconds. As in 1 of ten bullets will hit a rain drop. Realistically they aren't going to hit an entire raindrop. Lets say 1 in 20 hits an entire rain drop, 1 in 20 hits 1/2 a rain drop, 1 in 20 hits 1/4 of a rain drop. Just a hypothetical breakdown, but it goes to show that more than 1 in ten will hit some sort of water.
I'm still not worried about the waters effect though.