I've read from different sources (can't find them online) that firing a bullet at different angles from horizontal will result in differing amount of bullet drop.
For example, a gun is fired at a target 2000 yards away horizontally. The bullet drops X inches. Again the gun is fired at a target 2000 yards away with a 30 degree angle upward. The bullet drops Y inches. X does not equal Y. Same scenario, only 30 degrees downward angle. Bullet drops Z. Z does not equal X or Y. Why? What is happening? The bullet is fired at the same speed at the same distance, the bullet should be in the air for the same time. Acceleration due to gravity is a function of time, so the bullet should drop equally in all cases. Right?
The only change in each case is the angle gravity acts on the bullet. My guess is that when the bullet is fired upwards, gravity is pulling it downward, thus slowing the bullet down causing it to be in the air longer and increasing the drop.