Are apparently as unique as fingerprints or DNA. With millions and millions of guns in world I find it fascinating that no two can ever produce the same markings on a fired round, heck out of all the forensics shows I've watched I've never seen them say it's inconclusive. It either matches or it don't. Is it just a natural byproduct in the manufacture of the gun or is the manufacturer doing something to insure each gun is unique? Has a claimed match ever been reversed? I have read some DNA labs will come up with a match that turns out not to actually be a match due to poor lab practices. Inquiring minds and all that.

I have never watched an episode of CSI, so I don’t know what the current state of the claimed art is, but it’s hard for me to imagine that an ethical examiner wouldn’t consider the physical condition of a firearms barrel and sometimes state that no conclusion from a test would be possible.

I’m thinking of something like a gun that’s recovered from salt water and the bore is heavily rusted. I believe that for a match or “doesn’t match” determination to be made the two test bullets must be fired from barrels that are in generally the same condition. If the barrel has obviously been subjected to gross changes in condition, then we wouldn’t expect a match, but neither could anyone say with confidence that two bullets were not fired from the same barrel. There are other types of forensic examinations, e.g., fingerprint exams and polygraphs, that lead to “inconclusive” results, so why not firearms analysis?

And FWIW, the validity of certain criminal forensic examinations have come under attack in recent years. Some I believe are simply efforts by defense lawyers and “civil rights” activists to not only attack the criminal justice system in general, but also to get their moment in the sun. Unfortunately, much more attention is paid to something that challenges one of society’s accepted truths than the rebuttals that confirm them. That said, I consider the purposes polygraphs are still employed for to be little better than examining sheep entrails, and liking to think that I’m open-minded without letting my brain fall out, I believe that the validity of any forensic examination should be subject to examination itself.

Added: Now that I think about it, I am pretty sure that “inconclusive” results have been offered in some cases about Glock pistols due to the smoothness of their polygonal rifling that does not leave striations to be examined and compared. That would be especially true with a unjacketed lead bullet.

Another question is what a “match” means. That word would usually indicate that two test bullets were fired from the same gun. On the other hand it was once explained to me that there could be a “possible” conclusion based on things like the number and dimensions of the lands and grooves. Even if the fine markings aren’t enough for an exact match or doesn’t match determination, if one bullet was marked with two lands at a 1/12" twist rate and another bullet was marked with six lands at a 1/10" rate, then it’s obvious that they weren’t fired from the same barrel.

But if the gross dimensions are all the same but an exact match cannot be determined, it can lead to conclusions like, “The recovered bullet has the general characteristics of those fired from certain Smith and Wesson handguns chambered for 38 Special or 357 Magnum.”

Here's an article about a paper about a method for matching fired cases (not bullets) to the gun. Their complicated method had no false matches on their test set of 135 cases fired from 21 9mm pistols ("mostly consecutively manufactured" according to the article).

https://www.nist.gov/news-even...earms-identification

Here's an article about a paper on bullet matching. They took 10 consecutively manufactured Glock 9mm barrels and shot a bunch of bullets through them and sent them to a bunch of different firearms forensic examiners in different states. The fired bullet was matched to the correct barrel 98.8% of the time.

https://nij.ojp.gov/topics/art...ool-mark-examination

I am actually genuinely surprised that degree of accuracy is achievable, ESPECIALLY given how challenging they made the test sets (firing from the same model manufactured around the same time). I thought it didn't work that well in real life.

That doesn't mean that in practice, everybody is always right. This 2009 article mentions the Detroit Police Department's crime lab being shut down after a state audit found a 10% error rate in ballistics identification.

https://www.popularmechanics.c...ealth/a4548/4325797/

If the "science" allows "matches" of an acceptable level of accuracy, why the need for micro-engraving promoted by the anti-2A crowd? Obviously, this is another nonsensical "common sense" law designed to achieve a purpose other than what is being proposed.

Maladat, thanks for posting those very interesting articles. They really changed my opinion about the accuracy of such testing.

Thanks, maladat, for those articles.

quote:

Originally posted by architect:
If the "science" allows "matches" of an acceptable level of accuracy, why the need for micro-engraving promoted by the anti-2A crowd? Obviously, this is another nonsensical "common sense" law designed to achieve a purpose other than what is being proposed.

Don’t know for sure, but I’d think a whole host of things could change the fingerprint eg wear, fouling, dirt/sand, etc etc. Any criminal with the IQ over room temperature tapwater will figure this out.


I have polygonal rifling in Noveski barrels which I’ve always liked because they don’t deform the bullet very much, yielding very accurate and consistent results.

quote:

Originally posted by architect:
why the need for micro-engraving promoted by the anti-2A crowd?

No, I’m not supporting the microstamping push, but there is a significant difference.
Knowing the serial number of the gun that fired a cartridge would often allow the owner to be identified through FFL records.
Matching a recovered projectile or case to a specific gun requires that gun be available to provide the projectile or case to be compared against.

I.e., finding a cartridge case with the serial number of a gun that I purchased at the scene of a murder of someone I’d been seen arguing with would be a significant piece of evidence in the decision to charge me with the crime.

Finding a cartridge case without the microstamping at the scene of a murder (very common) but without having a suspect gun to compare its cases with is of no value.

Architect and maladat, do you realize that your avatars are no longer loading?

Most experienced criminals will use a gun once and then get rid of it. Kinda makes the tracing thing null and void. Anytime you read "he was found in possession of a gun used in a previous crime", think dumbass. And sometimes the dumbasses will use the gun and then give it to another dumbass.
Be glad most criminals fall into to the dumbass category!

I have seen some materials developed for lawyers concerning real-world accuracy and consistency of ballistic forensics, and that suggested that the accuracy of matches isn't all the police lab boys would have you believe. I'll see if I can dig that article up again.

Good articles maladat and thanks for the other responses as well. When I mentioned forensic shows I was not referring to the dramatized shows but the documentary ones. I think the only times I have seen them not be able to determine a match is if the bullet fragmented into too many pieces. Otherwise they seem to claim 100% ability to match.

Read the article about matching bullets to the consecutively manufactured Glocks.

I'd have liked further clarification of what "consecutively manufactured" barrels actually means, unless I missed it.

Does it mean 10 individual barrels that were pulled off the line which were all cut with the exact same broach? (Given Glock's volumes, I'm assuming they have more than one machine that broaches barrels.)

Or does it mean they took 10 Glock pistols with consecutive serial numbers and tested them and which, therefore, may well not have been made on the same tooling?

quote:

Originally posted by Oat_Action_Man:
I'd have liked further clarification of what "consecutively manufactured" barrels actually means ....

My thoughts as well.

I’m not a gunsmith, and definitely not a Criminalist, but wouldn’t running a rat tail file up and down a gun barrel change the lands and grooved markings enough to no longer make a match possible?

One problem with a lot of this kind of science is that it is fairly empirical. There isn't a lot of double blind testing, and statistical analysis to see how it holds up over large numbers of samples.

I am not saying that the studies quoted above have this defect, as I do not know. They seem to be trying to correct this defect, in fact. But of lot of forensic science, in general, is not as rigorously tested as it should be.

That is hard to do. You'd have to shoot dozens of different bullets into dozens of different media from dozens of different guns. You have to keep track of all those bullets, and then see if an examiner can reliably match a bullet to a given gun, blind. Or under which sets of circumstances is it possible, and which make it harder.

This would be a huge product, and an expensive one. In the forensic sciences this is often not done. The prosecutors have little motive to get this rigorous science done, as the system now works pretty well for them.

That makes sense Mr. Tanner. If you want to keep the gun after the crime, have a spare barrel in stock that you can swap out with the barrel used in the crime. Shame to throw away a nice Sig 226 SAO legion, right?

You would also have to toss out the slide as well as the barrel. Marks left on the case by the ejector, breechface and extractor all leave identifying marks.

^^use a grinder and don’t just yeet it into a river..some YouTuber will be along with a go-pro to find your heater

For the record, all comments in this thread that purport to guide anyone in a method to obscure the use of a firearm in a crime are NOT guidance. The comments are conjecture, offered solely for entertainment purposes, and are based in no way on any actual experience or expertise.