A bullet fired straight up into the air will reach a peak of 0 fps. As it begins the return to the earth there is nothing but gravity causing its return.
The fastest this bullet can travel is terminal velocity.
A bullet can travel very fast downward assuming it can be shot high enough in order to reach terminal velocity through all the atmospheric conditions.
All the theory based math equations are great, but they still dont trump basic high school science. 
Of course there are variables that come into play (height, and mass).
