This will sound stupid at first but bear with me. How long (time wise) does a bullet fly when fired straight from you (parallel to the ground)?
Less than a second.
I know, it depends on the velocity, sectional density, ballistic coefficient, etc.
The forces at work to pull a bullet to the ground work the same whether it is a 230 gr. FMJ fired out of a 1911 at 850 fps and a 52 gr BTHP fired out of a .22-250 at 3200 fps. The primary force is gravity. Gravity is a constant force on Earth. It is normally expressed as 32 ft/sec/sec. That is to say an object falling toward Earth will gain 32 fps of velocity every second.
If the bullet was fired from a (Parallel) muzzle that was six feet off the ground it would hit the ground in less than 1/4 of a second. It does not matter how fast it was going when it exited the barrel. Gravity is constant. It works on all matter the same.
If you were to fire the bullet from 32 feet above the ground it would hit the ground in one second.
This is a hard sell for some of us who have magical impressions of what bullets do while in flight. They do not create lift. They do not rise above the barrel at some point. They fall to the ground.
Now, most of you will realize the barrell is not pointing parallel to the ground when we shoot. The barrel must point up, slightly, in relation to the sights (Scope etc.) for the bullet to impact at the same spot at two different points down range.
With that said lets get back to the problem at hand. How can I insure I do not shoot my hunting buddy. If you are hunting from an elevated stand, most of your shots will be slightly downward. If you were in a 32 foot high stand shooting at a deer with a downward trajectory, the bullet will be in the air for less than a second.
Terrain will have a lot to do with the problem. If you are shooting upward at a deer the bullet may be able to go over that canyon rim and hit someone a mile or more away.
Are you now more confused? That does not really answer your question but raises a whole new set of questions. Now you have some real questions to ponder.