Primary and secondary markings over metal bullet help in?

Markings on the bullet are used to identify the gun used. Bullet finger printing -Study of comparison of markings on crime bullet & test bullet under comparison microscope Primary Marking/Class Characteristics: Produced by rifling groovesQ * Primary markings are used to identify the make & model of the guns involved. Secondary markings or individual/accidental characteristics Produced by irregularities by manufacturing process are different for each gun produced by same manufacturer. They are useful in identifying the specific gun which was fired.