This can reveal the make of the bullet and what the bullet hit. It can also reveal the velocity of the bullet which can provide information on the type and power of the gun used. Additionally, the shape of the bullet can show the distance from which it was shot. Was the crime committed up close, or from across the street? Striations or other marks can indicate the type of weapon used in the commission of the crime.
One possible defence at a criminal trial would be to suggest to the examiner that the bullet in question is a very popular one. Some bullets are manufactured in the hundreds of millions. They may not be as much of a signature as an examiner suggests. Some bullets are very common. It can be hard to trace them back to any particular gun. Examiners should generally be cautious about reading too much into a found bullet. It is unlikely to provide a complete blueprint to the