Begin with the desired range, measured in yards, to determine the drop, velocity, energy and time with which a .223-caliber bullet reaches its target. Bullet weight, casing and velocity of the bullet upon exiting the barrel of a gun also affect a given bullet's trajectory.
Trajectory charts typically measure bullet drop in inches, velocity in feet per inch, energy in pounds per feet, and time in milliseconds. Bullet trajectory charts make use of a number of fixed variables to determine the drop, velocity, energy and time of a bullet's trajectory. In addition to bullet weight, casing and exit velocity, charts generally assume the presence of a standard size scope mount to accurately calculate drop. Trajectory charts typically do not take atmospheric conditions into consideration, but more advanced ballistic calculators do.
Using a .223 trajectory chart requires knowledge of all fixed variables and the distance of the target from the barrel of the gun. For example, a .223 metal-cased Remington round weighing 55 grams and exiting the barrel with a velocity of 3,215 feet per second reaches a target 500 yards away in less than a second, dropping approximately 64 inches and losing 1000 pounds per feet of energy in the process.