This makes the bullet spin as it passes down the barrel, but it leaves tell-tale marks on the bullet that are unique to that particular firearm. The presence of rust or spider silk indicates the gun has not been fired recently. At close range, particles from a wound may lodge inside the barrel. .
This information is extremely important to the manufacturers of the ammunition and weapon. The ammo manufacturer must design ammunition that works properly in the weapon. The shellcase must be strong enough to handle the pressure and there must be enough pressure for the weapon to function properly. The gun manufacturer must design the gun with enough strength to handle the pressure and function reliably with any type of ammunition. .
Internal ballistics also yeild another benefit--ballistic fingerprinting. When a gun is fired the round leaves a unique fingerprint of scratches and dents on the shell's casing. Every law enforcement agency use these the unique signature of the "fingerprint- to match spent rounds and casings found at the crime scene. They, the law enforcement personnel, hope that the fingerprints will lead to an arrest.
The internal ballistics of a weapon is not that important to the average gun owner. He or she probably does not care about the markings on a bullet or how sturdy the gun barrel is, but mainly what happens when the round leaves the chamber. .
External ballistics is the study of what happens between the time that the projectile leaves the barrel and it hits the target. Velocity, trajectory and accuracy are the most important parts of exterior ballistics. .
External ballistics is concerned with the motion of a projectile while in flight and includes the study not only of the flight path of bullets but also of bombs, rockets, and missiles. All projectiles traveling through the air are affected by wind, air resistance, and the force of gravity. These forces induce a curved path known as a trajectory.