Originally Posted by tugg
the rule of 15's is pretty close but it still occurs slightly closer.
Under 15 yards (no matter what the angle) 0-90 degrees up or down, the difference in trajectory is so small you won't be accurate enough to be able to tell (if we're talking purely ballistics).
If you've witnessed anything different, it's not ballistics that's the problem it's likely to be that at extreme angles, the problem isn't knowing where to aim, it's keeping your crosshairs steady and dealing with cant / parallax error etc.
Unless you're shooting a springer and they do very weird things.