Almost by definition, any shot which doesn't hit the shooter's intended target is guaranteed to behave in a manner the shooter didn't intend. Further, because the bullet won't be traveling along the shooter's line of sight, it will commonly end up going someplace the shooter can't see (since his view will be obstructed by the intended target). Is there any particular reason to believe that a bullet fired at a slight downward angle would be more likely to harm someone other than the intended target than would one fired horizontally or at a slight upward angle?
Yes.