Ballistic fingerprinting has been used as evidence in US courts and elsewhere. In this method found bullets are compared based on markings the firing gun left on them. This should allow to prove which gun a certain bullet was fired from.
I've heard about several forensic techniques that were widely used but were not substantiated by evidence, e.g. a certain way of determining if a fire is arson. In the linked article it is also mentioned that some lawmakers want to abolish the database of ballistic fingerprints as it is claimed to be ineffective.
How good is the evidence for ballistic fingerprinting? Specifically,
- How often are the projectiles undamaged enough to allow ballistic fingerprinting?
- How high is the false positive rate, projectiles identified as belonging to a certain gun that weren't fired from it?
- How high is the false negative rate, how often is no match found if the correct projectile and gun are compared?