A case of murder with gunshot is repoed. A metal bullet is recovered from the body. Primary and secondary marking on a metal bullet can be used for -

The synopsis of forensic medicine & toxicology ; Dr k s narayan reddy ;28th edition ; pg.no. 135 The firearm leaves their signature on the caridge case & on the bullet .With all rifled firearm the bullet is slightly larger than the barrel & as it passes through the barrel ,its sides are marked by the rifling of the barrel (PRIMARY MARKINGS ) .They are mist useful in identifying the make & model of gun involved .The surface of the bullet is also grooved by irregularities on the inner surface of the barrel itself (SECONDARY MARKINGS) which are specific for that paicular weapon.