If you were to drop a bullet at the same exact time you pulled the triger on a gun and the gun was pointed exactly flat the bullets would hit the ground at exactly the same time. The faster the bullet is traveling when it leaves the barrel the farther it will travel, but the time of flight will be the same. Gravety pull things down at the rate of 32 ft. per second per second. So at the 1 second the bullets will be falling at the rate of 32 ft/sec. and will have fallen 16 ft. At 2 sec. the bullet will be falling at the rate of 64 ft./sec. and will have fallen 32. ft. If the gun is pointes up or down alittle every thing changes. As a rule the center of your scope is aprox. 2 1/2 inches over the center of the bore of your gun. So if you are aiming at a target where your line of sight is exactly level then the center of your rifle bore is 2 1/2 in low. So to hit the target your bore will be pointed up alittle bit and the bullet will come up 2 1/2 inches to hit the target. It would be very easy to figure how far the bullet would travel except we also have the resistance of the air slowing the bullet down. How much it slowes the bullet down depends on the diameter of the bullet, the larger the greater the resistance will be. The weight of the bullet, the heaver the bullet the better it will retain it`s velocity. The shape of the bullet also comes into play as pointed bullets will cut through the air better than flat nosed bullets. With all of these thing haveing an effect on how fast the bullet will lose velocity and people being lazy, for the most part, some math genious worked out a formula where the all of these factors could be rolled into 1 number, and called that number the Blastic Coefficient. Useing the BC of the bullet it is easy to plug into other simple formulas, along with the velocity, and get the trajectory, and the maximum point blank range of the bullet. ( The max. range you can zero for where the bullet will be no more than 2 1/2 in above or below the line of sight. 2 1/2 in is what is usually used for varminit rifles.) I could go on and write a book on it, but several other guys already have so I`ll let it go here.