10/19/12 show matching the case to the gun is total BS

I copied this from Wikipedia

Databases
Some localities, particularly Maryland, have attempted to build up a large database of "fingerprints"; in the case of the Maryland law, all new firearms sales must provide a fired case from the firearm in question to the Maryland State Police, who photograph it and log the information in a database. The Maryland State Police wrote a report critical of the program and asking the Maryland General Assembly to disband it, since it was expensive and had not contributed to solving a single crime.[3] Subsequently however, the database did provide evidence used to obtain one murder conviction at an estimated cost of 2.6 million dollars per conviction.[4]

A California Department of Justice survey, using 742 guns used by the California Highway Patrol as a test bed, showed very poor results; even with such a limited database, less than 70% of cases of the same make as the "fingerprint" case yielded the correct gun in the top 15 matches; when a different make of ammunition was used, the success rate dropped to less than 40%.