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Old April 10, 2021, 04:26 PM   #1
TXAZ
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Barrel forensics (ok it's a movie)

Saw the tail end of a movie, where the suspect happily surrendered his weapon (same caliber as the murder weapon) to the police for forensics testing, and it came back a match for the caliber but negative for his gun....

But he did it with that gun as we found out in the end proudly displaying the gun to a friend, but you don't know how.

I'm guessing he either swapped the barrel (can a glock / S&W / ?? barrel fit in some other brand ?), or possibly sanded / slightly machined the inside of the barrel after the murder.

Any hints?
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Old April 10, 2021, 05:04 PM   #2
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I'm sure you could change the rifling imprint on a bullet by running a piece of extra fine sandpaper down the bore. That is if you wanted to keep the gun for some reason. Or of course change the barrel. This is the reason micro printing on the end of a firing pin would never work. Swap out the firing pin, or even run the tip over a piece of sandpaper.
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Old April 10, 2021, 05:21 PM   #3
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Quote:
Originally Posted by TXAZ View Post
Saw the tail end of a movie, where the suspect happily surrendered his weapon (same caliber as the murder weapon) to the police for forensics testing, and it came back a match for the caliber but negative for his gun....

But he did it with that gun as we found out in the end proudly displaying the gun to a friend, but you don't know how.

I'm guessing he either swapped the barrel (can a glock / S&W / ?? barrel fit in some other brand ?), or possibly sanded / slightly machined the inside of the barrel after the murder.

Any hints?
I worked on a case where a woman was charged with murder and the ATF and CBI crime lab affidavits stated that her Glock was the murder weapon. After my report, the prosecutor was forced to withdraw both expert reports and affidavits from those agents and then the case was dismissed. It was years later that the actual murderer confessed to get out of a life sentence in another case.

Yes, forensic evidence is difficult to prove, even with a probable match, unless a murder weapon is recovered at the scene and linked, by other means, to the accused as well. Beyond a shadow of a doubt (from criminal) is a VERY high threshold to meet. More likely than not (for civil cases) is a phenomenally easier threshold to meet.

I'll not go into specifics on the hows, but it is not that complicated to make a gun not match forensically even if used to commit a crime and recovered after the fact by LE. Fortunately, most crime is not committed by those with enough knowledge of the subject to do so.
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Old April 10, 2021, 07:47 PM   #4
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I'm guessing he either swapped the barrel (can a glock / S&W / ?? barrel fit in some other brand ?), or possibly sanded / slightly machined the inside of the barrel after the murder.
Are we to assume that the firearm in question was some type of semi-automatic, not a revolver for which a barrel swap would require unscrewing the barrel from the frame and then screwing in the replacement barrel and then fitting the barrel-cylinder gap?

If so, why would the new barrel have to be from a different make? In general you can't put barrels from one make of gun into firearms of another make (unless you're talking about guns like 1911s or Hi-Powers, where there are multiple manufacturers all producing guns from the same design). But you can certainly put a barrel from one Glock into another Glock, and you can buy aftermarket barrels for Glocks. I don't know if aftermarket barrels are widely available for other, newer semi-autos, but it's probably only a matter of time.
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Old April 10, 2021, 09:57 PM   #5
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Beyond a shadow of a doubt (from criminal) is a VERY high threshold to meet. More likely than not (for civil cases) is a phenomenally easier threshold to meet.
It’s proof beyond reasonable doubt, not “shadow of a doubt” (which is no kind of legal standard). “Reasonable doubt” is what often gives weight to forensic examinations, but reasonable doubt is still a very high threshold to meet. Much higher than the civil case standard of “preponderance of the evidence” (basically more likely than not) standard. To be completely fair, I don’t know of any criminal conviction personally based solely on projectile forensics matching a specific weapon. That fact is usually icing on the top of other (usually good, sometimes mediocre) evidence.
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Old April 10, 2021, 09:58 PM   #6
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TV bs aside, it is incredibly rare for the lab to state definitively that bullet exhibit A came from gun exhibit B.

You have to listen/look closely at exactly what is said. What is usually said is that the rifling pattern (LH, 1 in 18 turn etc) is consistent with being fired in the gun.

Note they do not say it WAS fired in the gun they say it is consistent with being fired in the gun, and the prosecutor then states that it was fired in the gun to the jury (note, prosecutors are not under oath) omitting that fact that it is also consistent with being fired from any other of the thousands or millions of guns with that particular rifling pattern.

Go watch My Cousin Vinnie for a good, and humorous look at how statements of fact are turned and twisted in Court.

Long time ago, there was a Columbo episode where the killer rebored the barrel of the gun he used, so it wouldn't "match" Columbo figured it out and hung him on the match between the gun metal and the shavings in his machine tools. (always felt that wouldn't stand up in court, but hey, its a tV SHOW)
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Old April 11, 2021, 02:01 AM   #7
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If you sand or rim the barrel, doesn't that destroy the accuracy of the gun? Why keep the gun? Might as well dump it.

Also, don't they look at other things like the ejector marks, the firing pin indent and even the imprint of the breach face? You are going to have to modify a lot of things. Might as well dump it and buy a new one!!! Take the gun apart, dump pieces in different places so it will never be put back together.
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Old April 11, 2021, 03:55 AM   #8
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If you sand or rim the barrel, doesn't that destroy the accuracy of the gun? Why keep the gun? Might as well dump it.
If you're a murderer, you are probably less concerned about bullseye accuracy than you are about being able to make your hit and not get caught.
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Old April 13, 2021, 08:33 PM   #9
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Let's use Glock for example... you could replace your OEM barrel with polygonal rifling with an aftermarket barrel which is button rifled. Now I've never been in a forensics lab, and I'm thinking about this from the perspective of a gunsmith/machinist, but the marks left on a bullet from traditional button rifling and polygonal rifling could be different.

The case could probably be examined for expansion in the case of an unsupported chamber versus a fully supported chamber which is seen in some aftermarket match barrels.

I'm not positive that there are different rifling profiles available in terms of number of lands, twist rate etc. but that's another possibility.

What was the movie? Since you only caught the tail end, perhaps the canonical answer can be found on the internet somewhere.
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Old April 14, 2021, 01:07 AM   #10
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Seriously.. two glock polygonal factory barrels.. fire a 9mm jacketed hp bullet from each.. can someone really tell the difference?

If you fire ten glock 9mms.. can you tell them all apart?

Even if the bullet goes in to ballistic gel?

I assumed the factory barrels were very identical as far as it goes, or that given 10 factory barrels, many would be so close as to be undifferentiable.
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Old April 14, 2021, 02:18 AM   #11
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Barrel forensics (ok it's a book)

For what it’s worth, in Stephen Hunter’s first Bob “The Nailer” Lee Swagger book, Swagger is framed by a high tech, deeply nefarious, black ops organization for a sniper style murder. They took one of the bullets fired from one of his guns, paper patched it and fired it out of another rifle with a barrel bored out a few thousands. The original rifling would be all the forensics folk would find.

Don’t know if this would actually be possible or not.

In the story the rifling becomes moot as the bullet is so deformed and smashed up by its impact that no rifling match would be possible. Using other methods though, the forensics lab folk are still able to identify it as being fired from Swagger’s rifle with a 99.999% chance of being right.

Disclaimer: Stephen Hunter is one of my favorite authors and I would recommend, without reservation, his series of books about Bob Lee Swagger and his relatives and also “Master Sniper” and “The Day Before Midnight” but maybe not “Tapestry of Spies”.

P.S. "Point of Impact was made into a movie "Shooter" but I haven't seen it.
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Old April 14, 2021, 08:04 AM   #12
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99.999% by what other methods? It's FICTION, guys, and a lot of the "expertise" is like the tycoon told Travis McGee about his tax records: "Some of it is right, some of it is part right, and some of it just looks right."

Yes, you can paper patch jacketed bullets in a smokeless caliber, the rest just looks right.

P.S. A similar technique was used to frame comic strip private detective Kerry Drake. The crooks somehow got a bullet from his .38; patched it and loaded it in a "dueling pistol" to shoot somebody and incriminate Drake.
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Old April 14, 2021, 10:00 AM   #13
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Jim Watson: "Travis McGee", that's an old name from the past! Bought my own "Busted Flush". What gun did McGee use?
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Old April 14, 2021, 11:51 AM   #14
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Originally Posted by stinkeypete View Post
Seriously.. two glock polygonal factory barrels.. fire a 9mm jacketed hp bullet from each.. can someone really tell the difference?

If you fire ten glock 9mms.. can you tell them all apart?

Even if the bullet goes in to ballistic gel?

I assumed the factory barrels were very identical as far as it goes, or that given 10 factory barrels, many would be so close as to be undifferentiable.
I remember an article, late 1980's(?), where an expert forensic witness was challenged by having 10 brand new revolvers of similar make to the weapon in the trial. Test fired a number of bullets from each and tested to match to the actual weapon firing them. I don't remember the success rate of matching to the test weapons but it was way lower than 100%.

With less machining in poly barrels one might expect a lower success rate for essentially new weapons.
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Old April 14, 2021, 01:18 PM   #15
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What gun did McGee use?
None very much. The only one I recall was an otherwise unidentified French pistol because it had a good strong magazine spring.

I gave up on the series when Ol' Trav opined that while he sometimes needed a gun in his work, the average citizen did not and should not have a weapon.


There were police departments buying Glocks with "artifacts" in the barrel so they could identifiy bullets shot by their people. I don't know if all the barrels were the same or if they were individual to the gun/cop.
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Old April 14, 2021, 05:55 PM   #16
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99.999% by what other methods? It's FICTION, guys,
Yes, yes it is. And it should be taken with a grain of salt. BUT if you're willing to deploy a goodly amount of "suspension of disbelief" and stretch out your "limits of credibility" it's an enjoyable (IMhO) story.

In the book "Point of Impact" the government forensics expert is an honest guy and is honestly certain the killing bullet was fired from Swagger's rifle. He has done some chemical/atomic analysis voodoo on the copper in the bullet and the copper in the barrel of Swagger's rifle and determined that, yes indeed, the overwhelming evidence is that the bullet was fired from Swagger's rifle and he gets up on the witness stand and says so.

It's very important to the plot that the bullet is so mangled that it would be impossible to compare rifling marks. It's important to the plot that to preserve the voodoo analysis of the copper in the bullet to the copper residue in the barrel that the forensics guy won't let the rifle be fired again so as to preserve this evidence.

If anybody wants more info I'd encourage them to read the book. It's fiction, but IMhO it's pretty good fiction. Also it's quite possible I'm doing a disservice to Stephan Hunter by my description of the points in the book, that is, the book is probably much better than my description of it.

"Point of Impact":
https://www.amazon.com/Point-Impact-...8440660&sr=8-1
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Old April 14, 2021, 06:30 PM   #17
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I have 2 G19's. I could shoot someone with one of my guns, then swap out the barrel and slide and toss the other gun, along with the slide and barrel in a river. While the frame in my possession was the murder weapon, the barrel and slide were not. The forensics wouldn't match the bullet.

Since Glock puts SN's on frame, barrel, and slide, it would look odd having mis matched numbers. But you could do the same with other brands. where the SN is only on the frame.
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Old April 14, 2021, 11:06 PM   #18
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Mike Hammer did it every time he shot somebody who deserved it but the authorities might not agree.
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Old April 15, 2021, 06:30 AM   #19
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Yep, "Betsy" had two barrels.
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Old April 15, 2021, 02:18 PM   #20
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The general public has been thoroughly brainwashed by over a century of being told how ballistics can "match" a bullet to a specific gun. Our, and other governments have spent millions of $ because they were told a fired case can be matched to a specific gun, (and they believed it, for a while).

Generally speaking, a "positive match" is a very rare thing, and requires that there be something unique, and different about the suspect gun that is not found in other guns. Something in the barrel, or action that leaves a distinctive (meaning can be identified ) and unique (meaning not found in any other gun) that imprints onto the bullet or fired case.

ALL of which might mean NOTHING in a criminal case, or it could be the deciding factor, if the jury believes it to be.

And that is a key factor, what the jury believes, not what facts actually are. The triad needed for conviction is Means, Motive, and Opportunity.

Convince the jury that the accused had all three, and the jury MAY convict (and often does). Fail in "proving" the accused had all three and that is more than "reasonable doubt."

Many times, ballistic evidence is presented as positive proof when it is not. A lot of the evidence is akin to the paternity test that cannot prove that you are the father, but can prove that you are not.

Taking the fictional example use previously, where the bullet could not be matched to the gun by rifling marks, but was matched with "voodoo" analysis of the copper alloy residue in the gun barrel matching the copper alloy of the bullet.
Quote:
In the book "Point of Impact" the government forensics expert is an honest guy and is honestly certain the killing bullet was fired from Swagger's rifle. He has done some chemical/atomic analysis voodoo on the copper in the bullet and the copper in the barrel of Swagger's rifle and determined that, yes indeed, the overwhelming evidence is that the bullet was fired from Swagger's rifle and he gets up on the witness stand and says so.
Here we have a situation where the expert is on the stand sort of lying. Yes, he's entirely truthful about the match between the copper of the bullet and the copper in the barrel, BUT stating that the evidence bullet was fired from the evidence rifle is overwhelming evidence is a conclusion, not a fact.

All that can be proven from the copper being a match is that the rifle fired bullets made from the same batch of jacket material as the evidence bullet. How many bullets does a bullet maker make from an individual batch of jacket material? tens. hundreds of thousands? Millions???

its proof that barrel fired bullets from the same lot# as the evidence bullet, but NOT proof that barrel fired the evidence bullet. However, the prosecutor will claim it is proof, and absent rebutting evidence, the jury will believe them.

Think swapping out the barrel will get you off scot free? Maybe, but not necessarily. I saw one of the "true crime" shows where the suspect did exactly that. Killed a guy then replaced the barrel in his pistol. He did get convicted, even though they never found the barrel that fired the fatal shots. They found where the killer had bought a replacement barrel, and that was enough for the jury to convict, along with the other evidence.

Over the years I have spoken with many people who believed that, were they going to commit murder, they would use a shotgun, since ballistics can't trace the pellets...

When I explain to them that yes, the pellets can't be traced to a individual gun, it doesn't matter, and in fact, using a shotgun makes the prosecution's job easier.

Means, Motive, and Opportunity. To prove means, in this case, all the prosecution has to do is prove you have a shotgun. They don't have to prove that the pellets came from YOUR shotgun, like they would have to do for a rifle or pistol.

Rifling marks and other identifiers on bullets and cases can change over time. And, they can also be deliberately or accidently altered. Big difference between a gun recovered at the crime scene and one "discovered" to be the murder weapon years later when hundreds or possibly thousands of rounds have been fired through it since the crime happened.

Again, I point out that what the experts usually say in court is not a definate no other possibility kind of statement but something along the lines of "is consistent with" kind of statement. Sound like fact, is fact that its "consistent with" but isn't a clear statement that gun A did fire bullet B.

Again, I recommend watching My Cousin Vinnie for a good example of how, in court, facts that are true can be make to look like something that isn't true.
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Old April 15, 2021, 02:42 PM   #21
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My uncle was a homicide cop and I asked him about this very thing. This and a lot of other stuff too. He said just shooting the gun a couple hundred more times would change the striations marks in the barrel enough that it would be very hard to make a match between the recovered bullet and the barrel of the gun.

Also fire lapping, not sanding the barrel would change the rifling marks. He also said 22 bullets were hard to match up. Coated bullets were even harder and the Lubaloy coating used on some Winchester bullets were pretty much impossible to match to the barrel they were fired from. They would get a more positive match up from a fired case at the scene than the actual bullet.

He stated most of their murder cases were solved by the killer confessing or they had a witness to the killing. So in spite of the drama you see on TV most of the CSI type of work doesn't solve the case.

He stated he would much prefer to try and arrest a killer than a robbery suspect. He said the killer had it out of their system and didn't really want to kill anyone else but that a robbery suspect was way more likely to shoot or fight back to keep from being caught and arrested.
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Old April 15, 2021, 04:14 PM   #22
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What 44AMP says above rings true to me.

"The bullet found is consistent with a 9mm fired from a glock of this model. The defendant owns that same model." Okay, I buy that.

The bullets I have recovered from deer have been mangled from a little to fragmented. I really doubt someone can tell that's MY blackhawk. The twist rate, number of lands, sure. That makes sense.

This is one of the things that bothers me about entertainment. If you're going to tell a story to a huge audience, why not at least have your facts straight? My wife disagrees. "Who cares, it's just a story!" She says.

I care. People can be educated by stories. In the history of humanity, that's how we used to learn everything.
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Old April 15, 2021, 04:43 PM   #23
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Over the years I have spoken with many people who believed that, were they going to commit murder, they would use a shotgun, since ballistics can't trace the pellets...

When I explain to them that yes, the pellets can't be traced to a individual gun, it doesn't matter, and in fact, using a shotgun makes the prosecution's job easier.
I mentioned in my other post my uncle was a homicide cop. One case he had involved two white guys who were driving around in the black part of town and shooting people with a shotgun. And they got caught. Not because the cops could attach the shotgun they used to the recovered pellets but because of a prostitute.

It seems that one of the shooting victims was walking down the sidewalk when the shooters let go with a round. What the shooters didn't see was the prostitute that had wedged herself into some bushes to take a leak. She had a good look at the car and the shooters and was able to give the cops enough that they made an arrest.

My uncle had came to my local Walmart to buy shotgun buckshot because that was where the shooters supposedly bought their BS loads from. They were trying to find the same lot number so they could do a neutron activation test to try and match the same batch of buckshot pellets. But IIRC in the end the shooters just confessed to the shootings.

And does anyone else here when watching a show or movie try to identify the guns being shown? I do and after about the third gun I have named and given a little history of my wife says in a load voice, "I DON"T CARE"! And some people apparently don't care.
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Old April 18, 2021, 12:25 AM   #24
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There were police departments buying Glocks with "artifacts" in the barrel so they could identifiy bullets shot by their people. I don't know if all the barrels were the same or if they were individual to the gun/cop.
Glock polygonal barrels are notorious for leaving little to no unique signature marks. When taking the armorer’s course, our instructor talked about this and mentioned Miami barrels where MDPD worked with Glock on producing barrels for duty guns with identifying grooves so they could identify a particular officers weapon in case multiple officers were involved in a shooting.
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