Forensic ballistics is the science of analysing firearms used to commit crimes, including the analysis of bullets, bullet impacts, calibre and such things.

Rifling is the process of creating grooves in a gun barrel to spin the projectile as it is being released, improving accuracy and range. Useful when firing the gun itself, but also highly beneficial in forensics. The rifling process will leave distinct grooves and scratches on the bullet, unique to each weapon.

Ballistics can be split into four primary areas:

Internal ballistics – Studying the process accelerating the projectile

Transition ballistics – Study of the projectile’s behaviour after leaving the barrel

External ballistics – Studying the passage of the projectile through air

Terminal ballistics – Study of the interaction between the projectile and its target (eg. Flesh, wood, etc)

Ballistic fingerprinting is the matching of a projectile or a specific gun, often carried out by the study of bullet striations (those markings left by rifling). Before anything, simple decisions are made based on the calibre of the bullet. Clearly an important point as, for example, a 10mm bullet could not have been fired form a 9mm weapon.

Barrel rifling also varies among different manufacturers and models, varying in the number and shape of groves, the twist rate, and direction. For example, a Smith & Wesson gun uses a right hand twist, and an M16 rifle uses a 1 in 7 inch twist. Examining these striations can often help narrow down the make and model of a weapon used.

However it must be taken into account that the weapon originally used could be altered in some way. For example, the owner of the weapon could replace the barrel, meaning it would not match striations originally left on a bullet, even if that was the gun used to fire.

Databases

Some locations, generally in the United States, are building up large databases of ‘ballistic fingerprints’. As with current fingerprint and DNA databases, such a system could prove highly useful in the future. For information on the equations to work out bullet trajectories, visit this site.