Some of the class characteristics found on a fired bullet are (1) the caliber of the bullet (diameter), (2) the number of lands and grooves, (3) the twist of the rifling (left or right), and (4) the widths of the land and groove impressions.
On bullets, the class characteristics are the rifling specifications of the barrel from which the bullet was fired. ... In a barrel, the individual characteristics are produced by the random imperfections and irregularities of the tool or tools used to produce the lands and grooves, and by use, corrosion, or damage.
