View Full Version : Firearm Forensics: Tracing a 9mm to a specific Glock serial number

August 15, 2010, 01:05 PM
Maybe I'm missing something, but I understand many different gun barrels are mass produced with the rifling formed inside by massive presses, not the traditional rifling machines. The manufacturers talk about repeatability, uniformity, consistency, etc. To me that would mean very few differences in the finished product.

So after watching CSI, I have to wonder if a slug of interest is found, can forensics absolutely positively identify it from a specific unique weapon (ie it came out of THIS Glock 19, serial number xxxxxx), or is it just to a particular model "a Glock 19", or a brand in general?

Just curious.

Mike Irwin
August 15, 2010, 01:25 PM
Generally a bullet, if not too badly deformed, can be matched to a particular brand of handgun IF it's the standard factory barrel and not an aftermarket.

But, it can't be matched to a specific gun just with the presence of the bullet alone. You need the gun so that you can compare rifling marks on the bullet and any distinctive marks on the case, if that is available.

As for a serial number, sure, they can give you a serial number when they match a bullet or a casing to a particular gun, but not before.

August 15, 2010, 01:35 PM
What about the test-fired bullets?

You know, the two empty casings you get in the sealed envelope with a new gun? There were bullets in those casings at some point. What happens to them?

August 15, 2010, 01:44 PM
Some states require a bullet fired from a gun to be kept on file . So if you have a bullet from a crime scene you could match it to one on file. That assumes you have a bullet in good condition ! Bullet diameter and number and dimension of grooves and lands can identify manufacturer and type of gun. There are many variables .
One of the earliest books on forensics was written in 1935 by Julian Hatcher.Modern test methods can identify bullet material from a source, powder residue from a source.
Early Nyclad bullets wouldn't leave a good impression of rifling marks so they asked for and got a change change !
Like any other test it's not an absolute .

August 15, 2010, 01:48 PM
I think the premise of the OP's question was that if the barrels are mass-produced in a way that does not leave distinctive (unique) tool marks of the tooling used to form the rifling, then would forensics be able to establish positively that this slug came from this gun, even if that gun were available to be test fired so the slug could be compared to the slug in question?

In other words, is it the case with such mass-produced barrels that they would not have tool marks unique to each particular barrel? If that's true, then the marks imparted to the bullet would be the same for all barrels of that model.


August 15, 2010, 01:51 PM
I believe the test bullets is one of those things that turned out to be totally worthless. There are just too many test bullets on file to go through and compare, say all 9mm glocks to every 9mm glock bullet found in a crime. THink about how many 9mm Glocks there must be in your state.

I remember an AG or something having a press release about it earlier this year.

August 15, 2010, 03:48 PM
DD captured the essence of the question better than I did (and I can't figure out how the quotes work here so here is a fatfinger of his note):

DD said "In other words, is it the case with such mass-produced barrels that they would not have tool marks unique to each particular barrel? If that's true, then the marks imparted to the bullet would be the same for all barrels of that model."
Thanks DD

August 15, 2010, 04:09 PM
Given a fired bullet in good condition with no gun to examine, a good forensic tech could probably determine the brand of the firearm it came from but not much else. In the case under discussion, the technician could say that it came from a 9mm Glock but there's no way to demonstrate that it came from a G17, a G19, a G17L, a G26 or a G34.

Given a fired bullet in good condition AND a gun to examine, a good forensic tech might be able to determine if the fired bullet came from the gun in question. The idea is that even if two barrels come off the same machine, tiny variations in the manufacturing process and finishing process or in the way the barrels have worn from firing and cleaning since the guns were new will create tiny variations in the markings on the bullet.

We're talking VERY small differences. Like maybe a tiny grain of metal or other hard material got caught in one barrel during the manufacturing process and that is causing a mark on the bullet during firing. Or maybe a bit of abrasive material got stuck on a bullet jacket and scored the barrel when it was test fired at the factory.

August 15, 2010, 04:45 PM
Thanks, JohnKSa, great explanation. And so even if two barrels might start out absolutely identical in every way, through firing, cleaning, etc., the barrels will become unique and impart those unique characteristics to the bullets fired through them.


August 15, 2010, 05:37 PM
The general idea is that even though they're "identical", they're still different if you can look closely enough--even when "new". But since most guns are test-fired at the factory, they have already started developing individual characteristics before a buyer gets them even if they actually were essentially identical to begin with.

Of course, because (in most cases) we're talking about very small variations, it's also true that if a gun is used significantly AFTER firing the evidence bullet, the additional wear may alter the barrel to the extent that it may no longer produce test bullets that match the evidence bullet.

And all of this depends on an evidence bullet in good enough condition to do a comparison.

August 15, 2010, 07:07 PM
I once worked in a quality control lab for one of the largest chemical companies in the US. We analyzed not only chemicals but also inspected mechanical components. A source of amusement was some of the “evidence” we heard of in criminal cases—we kept our mouths shut and just went about our own business because the “evidence” almost always brought out a confession.

I’m reminded of the case I heard of (urban legend? I don’t know.) of the cops who wrote “He’s lying.” on a sheet of paper and put it into a Xerox. Each time they got a suspicious answer from the suspect they would push the copy button on their “lie detector” and show the suspect the paper. He soon confessed.

A little bit of electron microscope and a lot of psychology works wonders.

Glenn Dee
August 15, 2010, 07:29 PM
Firearms forensics is old technology. The science was challanged by Glock Polygonal rifling. In my experience... and this is just my experience. When a Firearm is fired it will leave unique markings on the projectile, and the casing. Every rifle, and handgun that have rifling that is almost as unique as a fingerprint.

Every firearm has a set of rifling characteristics. These characteristics are unique to manufacture. Some manufactures share closely similar characteristics. In other words if a spent bullet is found in good enough shape to recognize the kind of rifling... an investigator may be able to tell what make of firearm it came from, and equally important eliminate those that couldnt have fired it. He should also be able to tell the Cal., sometimes the manufacture, and kind of round it was.

Every firearm that was machined in production has absoloutly unique marks from those machined. The question pops up... If a batch of guns were machined with the same tools wont they all have the exact same rifiling? No... as each tool is used to change the shape on the gunmetal it becomes a little less sharp. Eventually the tool becomes dull enough to change, or re-sharpen. This is why every firearm has unique rifling, and can be identified through the rifling. As a gun gets older, and is fired many times the rifling does wear, and change. A fired bullet will still match the firearm that fired it. Even if over time the rifling does change, the basic characteristics will remain. In theory you may test a round fired from a particular gun, and 6,000 rounds later that round wont be a perfect match to the gun . But it will be assigned a 75% chance of having been fired from that particular gun.

All of this depends on the skill, tenacity, and experience of the investigator. It isnt done like they show it on TV. There's a lot more to it. If any of you find yourself in the unfortunate position of being in NYC with some time on your hands... Visit the NYPD musium.There is an exelent display on firearms identification.

Glenn Dee

Glenn Dee
August 15, 2010, 07:42 PM
Hello Clay

I also have heard that "URBAN LEGEND" tale. Maybe when copier machines were a new item. These days it probably wouldnt work. Well on most people anyway. I grew up an inner city street kid... And I knew what a copier was.

As far as evidence leading to a confession... It works on TV... but in the real world a confession is the second weakest form of evidence. Right behind the eyewitness statement. As is evidenced by the spate of people released based on new science. Most of them were convicted by confession, or eyewit testimony.

Ballistic evidence is some of the strongest available. DNA evidence is strong. Fingerprint evidence is strong. Any scientific evidence is stronger than a confession. Without getting into specifics, or legal arguments. Most professional investigators wont present until they have real scientific evidence.

Sorry I took things off topic.

Glenn Dee

August 15, 2010, 11:10 PM
I think the matching of slugs is just one part of the puzzle in a criminal investigation. In other words, if you had a heated argument with someone, were seen at the scene of the crime, AND the markings on the bullet found at the scene of the crime match the markings from the bullet from your gun test fired by investigators, then they have a case.

I've also wondered the same thing considering thousands of barrels are made using the same machinery. Perhaps the 10,000th barrel from one machine may be significantly different from the first, but I would think those made right after one another are nearly identical.

After leaving the factory, I'm sure scratches from cleaning and regular use add to the individuality of the barrel's rifling. So..... I'm back to square one.:rolleyes:

August 16, 2010, 01:21 AM
[Ballistic] forensics involve much more than just matching a bullet, via rifling, to a subject firearm. The recovered bullet(s) will also have case depth marks, power residue and power burn patterns that can be used to scientifically match it to a subject firearm located with or without discharged ammunition.

Empty casings also have numerous identification marks such as finger prints, firing pin strike indentations on primer, chamber marks and ejection dents that can be matched to a specific firearm, just to name a few.

The #1 best evidence is,..a credible eyewitness.

Glenn Dee
August 16, 2010, 07:09 PM
Gotta disagree with you there Los.. Even then best eye-wit is trumped by scientific evidence

I agree there is a lot more to ballistic evidence than just matching the round to the firearm. But much of it falls under chemical analysis, fingerprint analysis, machine-tool markings. Thats several other forensic disciplines.

Spanish James... One must understand that ALL eviednce is circumstantial.

Forensic investigators... no matter who they work for are never trying to make a case. They are, and must remain neutral. (Unlike CSI TV shows)

In my opinion, and experience... Eye witness evidence is the least reliable.
Not that people lie (of course they do), not that people make mistakes(of course they do) Not that people can be influenced ( they sure can) Of course everyone has perfect eyesight, and hearing ( how many eye glasses and hearing aids do you see in the course of a day)...

In defense of the Eye Witness though... When I was a newly made detective I inherited a huge newsworthy case. When we brought the case in we had quite a bit of forensic evidence and some admissions. And one absoloutly perfect unshakable eye witness. The best Eye witness I ever had was... A blind man.

Aguila Blanca
August 16, 2010, 09:35 PM
I must live in a cave. I know about new pistols coming with a fired case (or two, since I live in a state that doesn't ask the dealer to send one to the state), but I have never heard of any requirement to include a fired bullet with a new pistol. What state(s) has/have that requirement?

As to identifying the brand of pistol, a Glock should be fairly simple since Glocks use polygonal rifling rather than traditional lands and grooves. A bullet fired from a Glock will likely never be mistaken for having been fired from any other brand of barrel.

Gary L. Griffiths
August 16, 2010, 10:20 PM
A quick primer on forensic ballistics from a retired Army CID Special Agent who spent his last tour at the Army crime lab near Atlanta:

Spent bullets and cartridge cases (whether revolver or semi-auto) have both class and individual characteristics which may be used to link them to the type of firearm used, and the specific firearm used.

Examples of class characteristics would be number, width, direction and rate of twist of rifling lands (grooves in the fired bullet), and width of extractor markings or firing pin indentations on fired shell cases. Class characteristics will tell an investigator a lot about the type of gun involved in, say, a homicide, but not usually a single model of gun. For example, a firearms expert might examine a fired bullet and conclude it was fired in a 9mm Glock, but wouldn't be able to differentiate between a Glock 17 or 19. Likewise, a bullet fired from a .38 Special Smith & Wesson revolver would not be distinguishable as to the model number or barrel length of the revolver.

Individual characteristics are minute differentiations in the finishing of firearms due to final finishing operations, barrel crowning, and, as the weapon is used, damage caused by cleaning, firing, etc. These marks mean nothing if a suspect gun isn't available for comparison. BTW, the evidence bullet isn't compared directly to a suspect's gun, but to a bullet of the same manufacturer fired into a water tank. Each bullet will have tiny scratches, or striations on it, caused by scratches in the bore or the crown. The evidence and exemplar bullet are compared using a comparison microscope, and if sufficient individual characteristics match, the firearms examiner can testify as an expert that the evidence bullet was fired from the suspect's gun.

There are, of course, limits, and, as Mike said, a suspect using an aftermarket barrel might leave a bullet that wouldn't necessarily be identifiable to the type of weapon the suspect owned. Of course, any investigator worth his salt would seize any firearm of matching caliber owned by the suspect, and have it checked by the lab, just in case.

August 18, 2010, 12:24 AM
Glen Dee wrote in part:
Forensic investigators... no matter who they work for are never trying to make a case. They are, and must remain neutral. (Unlike CSI TV shows)

I will generally agree with that but there is the FBI "expert" that came up with the idea that bullet metal composition could place a bullet to having come from a specific box of ammo. NOT the lot of bullets but the packaged 50 round box of loaded ammo.

August 18, 2010, 01:01 AM
So the scene from The Dark Knight was still complete malarkey right?

A fragmented bullet fired into concrete, matching the fragments to make a coherent fingerprint?

Batman is kind of anti-gun I suppose, and they were just trying to scare you.


August 18, 2010, 11:28 AM
What about the test-fired bullets?

You know, the two empty casings you get in the sealed envelope with a new gun? There were bullets in those casings at some point. What happens to them?

I guess I'm missing something, but I have bought several new guns over the past few years, both rifle and pistol, and have yet to get one with an empty cartridge in the box.