I've always wondered this...

[audihenry]

I don't know whether due to movies or just being misinformed, I've always belived that LE or the govt. or whoever has a sample fired casing/bullet from every single weapon legally sold to citizens, the belief being that if a crime were to be committed with the weapon, it could easily be traced back to its owner.

Is this the case? It seems like a massive undertaking to be effective or possible at all. Or are bullet casings simply used to identify the general type of weapon, or the same weapon as used in different incidents, without some large database of fired shots?

[domokun]

The markings left on the casing is specific to a barrel and gun. If the gun can have its barrel replaced, it'll be hard to trace it down because the new barrel + gun would leave different markings on the case. These markings are as unique as fingerprints.

[audihenry]

Oh I understand that, but I'm wondering if there's a massive database somewhere of every single unique unaltered markings on every gun sold or whether that fact is simply used after a crime to compare similar crimes and so on?

[M. Sage]

No there isn't. IIRC, Maryland has such a system for handguns, but it's never been used successfully and the police are pushing to have it shut down so they can use the money for something that might actually work.

It would make no sense to have such a system because it would be huge, labor-intensive, and completely useless. The marks left are going to change over time (and with different loads, case materials and probably boxes of ammo) making finding the right gun from brass left at a crime scene an impossible task.

[audihenry]

Are the logistics of such a system just too overwhelming to be useful?

[Fjold]

Are the logistics of such a system just too overwhelming to be useful?

Yes,

[M. Sage]

Among other things... It's just pretty impractical whatever way you come at it.

[audihenry]

Okay, thanks guys!

[ohsmily]

I went to a forensic science seminar (for defense attorneys) and one of the speakers talked for an hour about ballistic "fingerprinting" and related practices. The thrust of her lecture was that despite the commonly held beliefs that not only does every barrel leave a unique mark on every bullet but also that you can easily match the bullet to that gun, the fact is that it is not an exact science nor is it a reliable method for identifying the gun the bullet was shot from. She also spoke at length about matching casings to a specific gun. Again, she provided quite a bit of evidence that this is a shoddy method for matching a case to a gun.

As part of her lecture, she posted several enlarged magnifications of rounds that were shot from different guns but had essentially the same markings. Apparently, the FBI is moving away from this type of investigation technique. According to her, ballistic fingerprinting is going the same way that lead alloy analysis (the practice of identifying that a certain bullet came from a particular batch of lead) did.

And NO, there is no national database of this information.

[sorensen440]

They can however get your prints off the case as most criminals are too stupid to prevent that

[packnrat]

just think how many months? Years it would take the fastest humdinger of a computer to check out just one cartridge. Pending all the known 38 guns had at least one cartridge on file.

[CSACANNONEER]

Thanks, I needed a laugh today.

[caldude]

It's easy to change the 'fingerprint' a gun leaves - change the barrel, take a file to the existing barrel or crown, etc. So a national database would be worthless.

[M. Sage]

It's easy to change the 'fingerprint' a gun leaves - change the barrel, take a file to the existing barrel or crown, etc. So a national database would be worthless.

... shoot it a bunch of times then clean it; shoot it a bunch of times and don't clean it; use a different brand (or lot or box) of ammo with different case material or pressure characteristics...

[Dr Rockso]

Computerized ballistic fingerprinting is unreliable