Simplistically, the downward acceleration will be the same. But, the shape presented to vertical motion by the bullets is different. One is on its side, the other one points down. Also, one is moving very quickly and has a disturbed airflow around it, which will affect its vertical drag.
So - I would not like to predict which would hit the ground first - too many unknowns.
Gravity is always the same. As long as the bullet is shot horizontally and not upward or downward, both will hit the ground at the same time. Obviously, the shot bullet will be hundreds of feet away, but horizontal velocity has no effect on the vertical velocity caused by gravity.