The time it takes for a falling body to travel a distance d is the square root of 2d/g, where g is the acceleration due to gravity (about 32.2 feet per second per second) . Assume your pistol's bore is 6 feet above the ground, then when the bullet is fired it will take about 0.61 seconds to hit the ground. If the muzzle velocity is 1,000 fps and assuming that velocity remains constant (which it won't, but just for the sake of simplicity) then the bullet would travel about 610 feet horizontally before it hit the ground. If the bore is less than six feet above the ground (certainly true for me) the distance would be less. In the real world, where the bullet's velocity does not remain constant, the distance would be less. If the muzzle velocity is greater or less than 1,000 fps then the distance would be correspondingly greater or less. So this is really just a ballpark figure.