Ballistic fingerprints – can’t they be changed?

There has been a call for a database of “ballistic fingerprints” of guns based on a sample bullet fired from a gun. But wait, can’t you just, say, take a screwdriver and randomly scratch the inside of a gun’s barrel. Wouldn’t that alter the “fingerprint”?

It doesn’t even take that much which would probably destroy the barrel and make it obvious it’s been tampered with. Merely cleaning a rifle barrel will effect the rifling marks on bullets. Copper deposits and powder fouling build up in the barrel so a clean barrel won’t leave the same marks as a dirty one. Wear and use of course change any “fingerprint” left on bullets and cases. Crowning the muzzle, a simple procedure where a tool shaves away burrs will also do it. The same is true of bolt faces and extractors. On many rifles such as AR-15 types and Savage bolt action rifles changing the barrel and bolt for new ones is a fairly trivial task that requires no specialized skills or machine work.

Those who call for ballistic fingerprinting don’t know much about ballistics, or firearms in general. This, of course, won’t stop some, including many politicians.

The only useful thing you can do with a spent round is to compare the casing and the bullet against others recently fired, and even this won’t yield useful results much of the time.

Yep. This is one of the things that really pisses me off about gun control laws. Also applies to the stupid “cop-killer bullet” nonsense.

And the best (or worst) part is how the politicians seem to be proud of their ignorance.

IMNA Gun or a Forensic expert. But I have done some computer image analysis and recognition, hence this post.

Mr. Moto, what you see visually is only a part of the truth. Just like you can hear two speeches sounding the same and can’t distinguish it, but a computer can. Similarly, you may not be able to tell the difference between two hair pieces but chemical analysis can.

The profiles (marks) on the bullet can be characterized by the following :

1> The height
2> The width
3> The depth
4> Spacing of the marks circumference wise
5> Spacing of the marks axial wise
6> Frequency of the marks circumference wise
7> Frequency of the marks axial wise
8> Statistical distribution of the marks

These are a lot of things which an ordinary human with naked eyes cannot see or relate. On the other hand a microscopic image coupled with an artificial intelligence algorithm (Artificial Neural Network for example) will be able to work out a correlation and possibly recognize a match.

This is on the lines of face recognition computer techniques being used nowadays to identify suspects in crowds.

If an forensic scientist wants to go deeper, he/she can do an elemental analysis of the inclusions on the bullet and thereby know the composition of the bolt hitting the bullet, the barrel elemental composition etc.

Just doing a fourier transform on an image or sound gives you knowledge of so many things which are difficult to fake.

Having said that, the above analysis will not be 100% fool proof all the time. But it will surely narrow down the suspects, just as in the face recognition.

This post is just from the scientific point of view and just MHO. I am not trying to preach whether gun owners should get the fingerprinting done or not.

I have read that, after a few hundred rounds, the “fingerprint” of a barrel will change enough to get past the best reader. A sniper would probably shoot that many just to stay sharp. I am not a gunsmith, so take my post with .047 grain of salt, eh?

Yep, not to mention common gunsmithing such as:

New parts such as a barrel, extractor, ejector, firing pin

Polishing breechface, crown barrel, etc…

To deal with this the government would probably need the guns to have new fingerprinting done each year, not to mention all the guns that are already in circulation (~250 million). I would imagine the cost would be much higher than the FBI’s current fingerprinting database - $640 million to implement for about 35 million prints.

After a while, each gun barrel becomes unique based on a large number of characteristics, and it is rather hard to change. There is no one overriding characteristic that does it - just like most other physica; evidences.

In Texas when you renew your handgun license, you have to be fingerprinted again because they say/claim YOUR fingerprints change. Unique does not mean constant. They may change but they will be close enough to get a match.

The problem with ballistic fingerprints is that the owner can change them. Most owners won’t bother and the gradual change can still allow a match.