Maryland and New York already require ballistic fingerprinting. So far it hasn't helped convict a single criminal in Maryland despite "fingerprinting" 17,000 guns sold since January 2000. New York hasn't had success either.

And there isn't likely to be success any time soon, according to the study.

The report included the test firing of more than 2,000 rounds from 790 pistols.

When cartridges from the same manufacturer were test-fired and compared, computer matching failed 38 percent of the time. With cartridges from different manufacturers, computer matching failed 62 percent of the time.

"Automated computer matching systems do not provide conclusive results" requiring that "potential candidates be manually reviewed," said the experts.

But the experts estimated a California database would grow by about 108,000 entries every year for pistols alone. "This study indicates that this number of candidate cases will be so large as to be impractical and will likely create logistic complications so great that they cannot be effectively addressed," they said.

The test-firing results only scratch the surface of ballistic fingerprinting's problems.