Carl N. Brown said:
When criticism of the Maryland system focussed on lack of results in solving crime, supporters pointed out that it had the effect of raising the price of handguns sold in Maryland, which they considered a good thing.
Don't forget it also cements registration in place with such legal requirements.
Tracking the marks made by guns obviously requires tracking the guns too.
A system to track marks in a database is also going to allow easy browsing of gun owners by make, model, serial number, address, etc
This also has a strong potential to introduce false leads, incriminating innocent people.
Let us say someone is killed. Investigators determine X firearm type fired the round.
While the science of specific guns over time with wear being matched is greatly exaggerated, matching a particular firearm model or narrowing it down to a couple possible models is much easier, as different guns use different rifling and are built differently. With some guns a range of models can have similar markings not even limiting it to single model types, but it does narrow down what it was quite a bit.
Now let us say the investigators wish to develop leads, and so look in their database to see who in the area legally has such registered firearm models.
They get several hits. Now multiple innocent gun owners are under scrutiny. If one of them also happens to have known or crossed paths with, or otherwise had some sort of possible contact with the victim they may even become a prime suspect.
All because they just happened to own a certain model firearm.
One of the primary reasons for "success" in "ballistic fingerprinting" has to do with the low number of guns typically being used in crimes, and so even entered in a database at all. So even though hundreds or even thousands of other guns would probably be close matches across the nation, only 1 of that particular model with those markings has been involved in homicides in X inner city against Y gang.
Another reason for success is the low round count between crimes.
Yet a hobbyist firing thousands of rounds is likely to have their specific gun change profile enough to match many different guns during the same time period.
When you start it may have similar markings to a handful of guns in one state or region, and during the course of wear begin to match several different guns in another state, and a year later no longer match the original guns, and now match several new guns. The marking change, the scratches change, the metal making the markings wears, changes angles of contact, etc. Take a really popular model firearm, and you can be certain the markings of many specific guns of that model will overlap, and cease to overlap, multiple times throughout the course of use and wear. Your gun may in fact become a "perfect match" for different guns used in crimes around the nation, cease to match those guns, and then begin to match yet new crime guns all throughout its lifetime.
Yet another reason for success is the experts simply stating their certainty it was that particular firearm enough to be convincing to a jury, even if hundreds of other guns across the nation would match they are unknown, not in a database, and not part of the case.
"Fingerprint" truly is the wrong term. A fingerprint is much more unique, and absent certain damage grows back in that same pattern. A fingerprint is also measuring the actual swirls and whorls, not the slight scratch you got on your finger doing some yard work, that will be healed a week later and have a different scratch or cut from some new project or maintenance. The cuts, callouses, wear and indentations would constantly be changing on your fingers.
Compare this with firearms and "ballistic fingerprinting", where it is those constantly changing scratches being used to "ID" the exact firearm, while the specific rifling or other major constants are the same for thousands of similar models and often a range of model firearms manufactured similarly.
The only way actual fingerprints would be similar is if you had thousands of people with the same fingerprints, and were trying to measure wear and scratches on those thousands of identical fingerprints to tell them apart. Which would be constantly changing on those otherwise identical fingerprints, making any database based on such scratches worthless over the course of time.
