Without air resistance: Both at same time
With: Dropped bullet, assuming it's oriented facing down. The bullet is more aerodynamic facing down, and thus has a much lower drag coefficient. Ergo, it feels the effects of air resistance less than the dropping, fired bullet. It will reach the ground a few fractions of a second earlier than the fired bullet... Alternately, if you drop the bullet parallel to the ground (ie, same orientation as the shot bullet), it'll also hit very, very marginally earlier. Air in motion behaves increasingly like a fluid as you increase the speed, and so the slipstream around the shot bullet should help to support it in midair and retard the falling.
Ultimately, however, these are all occurring with such a tiny, tiny time difference that it's technically impossible to ever actually observe the difference, I think. So for all intents and purposes, they hit simultaneously (unless the bullet is going VERY fast, it's VERY oddly shaped, or your experimental conditions are better than anything that you could ever feasibly observe without ridiculous funding).
With: Dropped bullet, assuming it's oriented facing down. The bullet is more aerodynamic facing down, and thus has a much lower drag coefficient. Ergo, it feels the effects of air resistance less than the dropping, fired bullet. It will reach the ground a few fractions of a second earlier than the fired bullet... Alternately, if you drop the bullet parallel to the ground (ie, same orientation as the shot bullet), it'll also hit very, very marginally earlier. Air in motion behaves increasingly like a fluid as you increase the speed, and so the slipstream around the shot bullet should help to support it in midair and retard the falling.
Ultimately, however, these are all occurring with such a tiny, tiny time difference that it's technically impossible to ever actually observe the difference, I think. So for all intents and purposes, they hit simultaneously (unless the bullet is going VERY fast, it's VERY oddly shaped, or your experimental conditions are better than anything that you could ever feasibly observe without ridiculous funding).
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