Ballistics

Getting a shell from a gun to a target should be pretty simple. There's really only two controls on most artillery pieces -- azimuth and elevation. And you've frequently got someone out near the target telling you how to correct, in case your aim is off.

So what makes it so hard to predict where the shell will land? There are a lot of factors to take into account:

• Interior Ballistics -- the gun and shell
  • Tube Wear
  • Propelling charge (temperature, moisture, uniformity)
  • Coppering -- shell residue left in the gun by firing at high-charge
  • Projectile weight variance
  • Manufacturer's tolerances
  • Ramming, for separately-loading ammunition (where the shell and propellant are jammed together just before firing)
  • Rotating band
• Exterior Ballistics -- after the shell has left the gun
  • Angle of elevation
  • Wind
  • Air density changes
  • Air temperature changes
  • Drift due to the spinning of the projectile
  • Rotation of the earth (especially for long shots)
  • Shell surface finish

All of these factors can lead to error. Some of the factors, such as aiming errors, cause a constant error to be applied to each shot. These errors are overcome by forward observer (FO) feedback: ("You're long..change the angle of fire.") Other factors are somewhat random and will cause each shot to deviate somewhat -- this is known as dispersion.

Introduction

Dispersion