Comparison of bullets and cartridge casings
The operation of firearms
The trajectory of bullets (External Ballistics)
Powder pattern versus distance determinations
The reconstruction of crime scenes that involve the discharge of firearms
The possibility of accidental discharge of a firearm
Issues Concerning the "Matching" of Bullets and Cartridge Casings
In 2009, the National Academy of Sciences (NAS) published a critique of certain methods used forensic science. The NAS was most concerned with the comparative techniques that are often employed in everyday casework. These techniques include firearm and toolmark comparison.
The issue is whether there is any scientific basis for concluding that given a few “matching” striated markings on the questioned and test objects (commonly bullets and cartridge casings), the examiner can state, with certainty, that a particular firearm, to the exclusion of all other firearms in the world, fired the questioned (evidence) bullet or cartridge casing.
So what are we talking about here. Please see the photos below that represent stated “matches” that I have reviewed.
Conclusive opinion testimony that these are "matches", in the opinion of the NAS, doesn't have a scientific basis and should not be included in the examiner's report. They suggested that scientific research be undertaken to determine the validity of these opinions.