Rarely has a QI episode garnered such an immediate response as the G for Gravity episode of series seven. Many of the questions were so counter-intuitive that many viewers were left incredulous: for instance, would a bullet fired from a gun and one dropped at the same time really land at exactly the same time??
under theoretically perfect conditions they would, but what about the
real world? As with most things, the real world tends to throw the
odd spanner in the works.
In the case of falling objects, the spanner in question is air resistance. For these bullets, the air resistance will be different because the shot bullet is travelling through the air much faster than the dropped bullet. That's not the end of the story, though, since the shot bullet will be rifled (spinning) and travelling through the air in the most aerodynamically efficient manner possible, whilst the dropped bullet may well tumble, changing the effect of air resistance on it.
However, calculations on the effect of air resistance show that it will only effect the time taken for the bullets to drop by a very small percentage. For this reason, any difference in the time taken for the bullets to hit the ground would most likely be less than the experimental error in measuring the times involved, and so would be very hard to see.
In conclusion, bullets that are fired/dropped in an idealised situation will hit the ground at the same time. In the real world, there may well be a very slight difference in the time taken to fall, but this will be so small as to be almost impossible to observe.