SO far we have only considered the methods employed in the identification of individual firearms by means of fired cartridge cases. But it may easily happen that the only bit of material evidence available is the bullet which has been extracted from a victim, and in such circumstances the task of identification must be effected by marrying this bullet to a particular weapon.
The general principle employed is exactly the same as that used with fired cartridge cases. No two barrels are microscopically identical, as the surfaces of their bores all possess individual and characteristic markings. In fact every barrel has its thumb-mark in exactly the same way that every breech face has its thumb-mark.
When a bullet is fired from a rifled barrel it becomes engraved by the rifling, and this engraving will vary in its minute details with every individual barrel. So it happens that the engraving on a bullet fired from one barrel will be different from that on a similar bullet fired from another barrel. And conversely the engraving on bullets fired from the same barrel will be the same. So the task of identification depends on matching the engraving on two, or more, fired bullets in exactly the same way as it also depends on matching the imprints on the bases of two, or more, fired cartridge cases.
And since some readers may not be familiar with the appearance of the engraving on a fired bullet I have included photographs of unfired and fired lead and
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