A case of murder with gunshot is being investigated. A metal bullet is recovered from the body. Primary and secondary markings on a metal bullet can be used for which of the following leads?

An examination of the size of the bullet and its weight and calibre, the number, size and direction of rifling markings on it; and the kind of metal it is made of will all give clue regarding the weapon used. With all rifled firearms, the bullet is slightly larger than the barrel, and as it passes through the barrel, its sides are marked by the rifling of the barrel (primary markings /class characteristics) and cause the bullet to rotate. The surface of the bullet is also grooved by irregularities on the inner surface of the barrel itself (secondary markings/individual or accidental characteristics), which are specific for that weapon.