Ballistics or TV BS?


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rskent
December 31, 2011, 07:09 AM
OK so Iím setting watching one of my favorite shoot em up cop shows on TV. And of course the send the slugs off to ballistics for examination just like they have done in every cop show since Dragnet.
I understand the concept of comparing differences in rifling and the imprints left on the bullet as it travels down the bore. But have you seen the bore on a modern cold hammer forged barrel.
Next time you clean your Glock, take a look inside the tube. I canít believe they get it so smooth in there. Add to that, you have a number of barrels coming off the same mandrel. I find it hard to believe
that you can tell positively without a doubt that a particular bullet came out of a particular gun. OK if the tube is damaged in some way sure. The barrel maker and caliber sure. If the bore is in good condition, how?

If someone around here has a bit of first hand knowledge, please enlighten me. The search button has failed me.
Steve

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The Lone Haranguer
December 31, 2011, 09:48 AM
I don't have first hand knowledge. If Abby Sciuto is a member here, perhaps she can shed some light. ;)

I find it hard to believe
that you can tell positively without a doubt that a particular bullet came out of a particular gun.
They are taking a bit of "dramatic license" with that. In the real world, I think they can only match bullets to particular bores with a high degree of probability. If a bullet is fired from a particular gun, captured under controlled conditions and examined at the microscopic level, they can get more of a match. But bullets found at crime scenes (e.g., imbedded in walls, where on TV they simply dig them out of the surface with a pocket knife) or in bodies are almost always deformed in some way. Fingerprinting and even DNA testing (on TV it is "DNA while you wait") only have a high probability, too. With DNA it might be 99.99998 percent or whatever, but it is never 100 percent.

But have you seen the bore on a modern cold hammer forged barrel. Next time you clean your Glock, take a look inside the tube. I canít believe they get it so smooth in there. Add to that, you have a number of barrels coming off the same mandrel.
It is a truism that no two objects on Earth are exactly alike. You can take two consecutively produced barrels off the same mandrel and find differences in them, not with the naked eye of course, but at the microscopic level. This can be matched, again with that high degree of probability, to the "engraving" on the jacket, much less so with a soft lead bullet.

jollyroger
December 31, 2011, 11:47 AM
Glocks, HK's and some other brands use polygonal rifling, which uses a series of flats which twist the bullet, rather than traditional lands and grooves. This should have no effect on the ballistic comparison, because the impression of the rifling on the bullet would still indicate the brand of weapon used. The inside of the Glock you are looking at may look smooth, but the analysis involves microscopic marks. A microscopic examination of the inside of the barrel would reveal unique aspects which produce these marks.

In order to make a successful ballistic comparison, you have to get the weapon shortly after the recovered bullet is obtained. The micro-markings produced by a barrel will change over the life of the gun depending on the round count, corrosion in the barrel, etc.

Deformation of bullets is a problem, but if a portion of the bullet is intact, such as the back portion of an expanded hollowpoint, sometimes that can be used. Comparisons are similar to fingerprint comparisons in that the examiner finds points of comparison which are consistent between the recovered bullet and the test bullet. If you get enough points of comparison, it is a statistical certainty you have the right weapon.

BTW, they can do great things with recovered brass too.

jdh
December 31, 2011, 12:02 PM
glock will make barrels with custom bore marking for agencies to allow them to tell if a bullet came from one of their guns.

HankB
December 31, 2011, 12:04 PM
Comparisons are similar to fingerprint comparisons . . . After having to have my fingerprints redone on two separate occasions when applying for and then renewing my Texas CHL, I've become very skeptical about forensic evidence. (If prints done by a technician under controlled conditions using an official fingerprint kit with a cooperative subject aren't good enough to complete a background check, I really wonder if prints recovered at a crime scene are good enough to obtain a conviction. Ditto for ballistic evidence.)

ants
December 31, 2011, 01:24 PM
The science in real life is called Tool Mark Identification. For a technician to practice it in a lab, certified education is required. Typically technicians attend AFTE training for certification, but other educational institutions offer coursework. We generally think the FBI takes the lead in such science, but for the FBI to take the role of Examiner and offer evidence in court it must separate itself from the basic science and technical certification. The AFTE and related forensic organizations provide that function.

The Daubert Ruling
The legal aspect is much more involved than it seems. In 1993, the United States Supreme Court changed a legal standard for those that provide scientific testimony. The new standard requires trial judges to be the ‘gatekeepers’ of expert evidence, not the FBI or prosecutors. Four criteria are used to evaluate testimony before it can be admitted.
1. Testability of scientific principal
2. Known or potential error rate
3. Peer review
4. General acceptance of the methodology in a particular scientific community.
Daubert essentially requires that examiners be able to explain how they reached their conclusions. They must be prepared to discuss all four criteria, including error rate and peer review by other examiners.

In addition to reading rifling marks, other tests are conducted (including residue and metal alloy) to substantiate the testimony. However, many of these tests have been declared unreliable. In fact, The FBI announced 5 yars ago that its lab had suspended bullet lead alloy analysis, which routinely had been presented as evidence to match bullets to a specific manufacturer and even to a specific manufacturing lot. The FBI announced that these tests are unreliable, and even participated in identification of wrongful convictions caused by faulty lead alloy analysis.


TV? They write whatever they want.

Reality? A lot harder.

mljdeckard
December 31, 2011, 01:51 PM
Take a criminalistics class and see how it works. The world is a whole new place under a 15-30x microscope.

All items which have been machined have unique tooling marks. You can cut a barrel into two sections, shoot bullets through each half, and tell which bullet came from which section. You can ID which pair of scissors cut a sheet of paper. You can ID which bolt cutter jaws cut a lock. You can ID which hammer smashed a lock.

gym
December 31, 2011, 04:07 PM
But how do you tell with some of this fragmenting ammo, and powerball where everything is squished together. I find it to be a very difficult thing to say definitivelly that a crumpled deformed piece of metal that hit several different things in it's path, came from a specific gun. If you cannot duplicate the exact same end result, it's not reliable, then we have shotguns.

Gunnerboy
December 31, 2011, 04:13 PM
I dare you to match my 00 buck to my 870s barrel :neener:

Chuck Dye
December 31, 2011, 07:21 PM
Explore the Association of Firearm and Tool Mark Examiners (http://www.afte.org/) web site and included links for a more realistic idea of what works.

MachIVshooter
December 31, 2011, 08:21 PM
glock will make barrels with custom bore marking for agencies to allow them to tell if a bullet came from one of their guns.

I've never heard of such a custom offering. Reference?

LibShooter
December 31, 2011, 08:25 PM
I don't have first hand experience with forensic ballistics, but do for writing and producing for TV. They have sixty minutes to tell a pretty complicated story. The audience has "signed on" to accept certain shortcuts to keep the narrative moving. "Ballistics" is one of them.

From what I do know about the science, ballistic evidence is more like blood type than DNA. It can't always tell you which specific gun out of millions DID shoot that bullet... but it often can tell you which ones didn't.

Zoogster
December 31, 2011, 08:38 PM
From what I do know about the science, ballistic evidence is more like blood type than DNA. It can't always tell you which specific gun out of millions DID shoot that bullet... but it often can tell you which ones didn't.


That is a fair analogy.

People who have a career wrapped up in the acceptance of a specific science will overstate the science. Understating it would readily put them out of a job.
The result is the experts of the field will vastly exaggerate the precision and certainty even when it is not quit that specific in real life.
For example the FBI used lead comparisons for decades, stating with certainty how precisely they could tell if a bullet came from one batch of lead or another.
After decades of convicting people with the assistance of this tool of absolute certainty they acknowledged it wasn't certain at all and dropped its use. You can bet some experts had to find a new field to make a living in at that point.

flatlander937
December 31, 2011, 09:00 PM
I imagine matching up anything on hollowpoints could be potentially far tougher to do than a standard lead or FMJ bullet?

David E
December 31, 2011, 09:20 PM
Consider, too, the ejected casing. It's typically not exposed to the same dynamics as a bullet.

Since we're talking Glocks, the same degree of inspection would be applied to a casing found at the scence of a serious crime. Characteristic markings caused by the ejector, breech face, firing pin indention, ejector and ejection port can go a very long way in determining which gun was used.

Vern Humphrey
December 31, 2011, 09:45 PM
Actually, both ballistic matching and fingerprints have never been scientifically proven. No one can state the odds that a particular match is that of the suspect or the suspect's gun -- as opposed to DNA, where the odds of a match can be stated with confidence.

MyGreenGuns
December 31, 2011, 09:56 PM
I remember reading somewhere that they were thinking about "microstamping". That would be microscopic serial number markings on the striking face of the firing pin. That way they could identify a specific gun by the spent casings.
The same article said it would be too easy for people to sand the numbers off, or fire the gun until the numbers no longer printed on the casings.
Many of my friends believe "CSI Ballistics" are real. They wonder how murders arent solved in 30 mins of finding a bullet.

jdh
December 31, 2011, 10:00 PM
Quote:
glock will make barrels with custom bore marking for agencies to allow them to tell if a bullet came from one of their guns.


I've never heard of such a custom offering. Reference?

Phil Goldsmith, Instructor Glock Armorers Course during the discussion of the polygonal rifling.

MachIVshooter
January 1, 2012, 12:27 PM
From what I do know about the science, ballistic evidence is more like blood type than DNA. It can't always tell you which specific gun out of millions DID shoot that bullet... but it often can tell you which ones didn't.


That is a fair analogy.

I agree.

As far as I know, not once has a crime been solved with only a bullet as evidence that lead to the gun and the criminal possessing it.

However, it is common to use ballistic forensics when the suspect weapon is already in evidence-they catch the suspect, he has a gun, they test fire his gun and compare markings.

The odds of matching a bullet to a specific gun out of thousands of the same model are virtually nil (see Maryland's abandoned multi-million dollar ballistic fingerprinting program), but as corroborating evidence, matching a recovered slug to the weapon found in possession of (or known to belong to) the suspect helps strengthen a case substantially.

The Lone Haranguer
January 1, 2012, 12:49 PM
Deleted, please disregard.

gpb
January 1, 2012, 01:26 PM
"glock will make barrels with custom bore marking for agencies to allow them to tell if a bullet came from one of their guns. "

Does that include agencies like the Crips and the Bloods?

Carl N. Brown
January 1, 2012, 01:53 PM
^It would make labwork easier, but I doubt if Crips and Bloods order from the factory. :)

Seriously though. Comparison to fingerprints is not valid. Fingerprints don't change over time. Forensic ballistics characteristics (individual barrel for the bullet markings, for casings firing pin, extractor and ejector) change with wear, tear, erosion, corrosion, accidents, repairs, replacement.

Ballistics comparisons that work are ballistic evidence at crime scene matched to gun in possession of suspect at time of arrest. With systems like NIBIN matching scanned crime scene evidence, that may clear more than on crime.

steelerdude99
January 1, 2012, 04:41 PM
While we are on the TV crime show BS thread, I recall an episode of Law and Order where there was an assassin who used a .380 and was a bit of a ďcheap skateĒ. They only busted him as he had a box of ammo that had a few rounds that were ďchamberedĒ in the same gun that was used to murder several persons. Supposedly, they had scratches on the brass that are unique to specific firearm. I would argue that the magazineís top edge would scratch the brass more so than the gunís extractor and ejector.

chuck

Tiberius67
January 1, 2012, 05:55 PM
The police have run dragnets for owners of a specific type of firearm or barrel...

A US Attorney in WA was murdered in his home with a Makarov that had a after market .380 barrel installed. The Feds went after the barrel maker and wholesalers to get the list of people who had bought them and then grabbed them from the owners for "testing". No luck so far.

During the DC sniper rampage, pretty much every caucasian owner of a Bushmaster AR-15 in the DC Metro area got visited by the Feds. If they didn't cough it up willingly, they got paper and sent in the JBTs to get it. No luck of course....because thier 'profile' of the shooter being a white right-wing gun-nut was a total fantasy, the real shooters were a pair of black muslims putting a jihad on the infidels.

The AR got me to thinking though....all someone like that had to do was buy a complete upper and mag, use those to do thier crime, then store those elsewhere and put thier original upper back on thier lower. They could have handed it over to the Feds for testing and been officially cleared then got back to thier murder spree.

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