Originally Posted by Wil Terry
YOU SIR, are in dire need of a copy of HATCHER'S NOTEBOOK where all such things you ask thereof are covered. IF it is not in there you have no need of knowing it.
+1 We have a winner.
For the questions posed;
If the gun barrel is parallel to the ground then the projectile will impact a relatively short distance from the muzzle. It will impact the ground the same moment an identical projectile, dropped at the same instant from the muzzle as when the shot is fired, will hit the ground. (yeah, I know there are variables such as wind resistance, but for the purposes of this discussion that answer will do nicely)
If you fire a projectile at a 90 degree angle to the earth, the projectile will reach zero velocity at some point and come back to the earth at a terminal velocity determined by a number of variables; does the projectile turn to point the nose (narrowest part) toward the earth or does it come down base (flat part) first? What is its sectional density and ballistic coefficient? Gravity will be pulling the object toward the earth and the air will retard its speed.
From memory, a .30 caliber military round will have a terminal velocity of around 350 fps.
As was stated, this is all in Hatcher's Notebook, which is not in front of me at the moment.