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Old 09-30-2016, 04:14 PM
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How do forensic matches work with shotguns?


Watching a cop show made me realize that matching projectiles to weapons with rifled barrels is plain enough but how do police ID smoothbore shotguns used in crimes?

If the shooter doesn't leave spent shells around and doesn't use rare powder/projectiles, how would the police go about making a match?

How reliable are matches based on firing pins or loading/extraction?


Need answer soon-ish, I'm heading to Reno next week.
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Old 09-30-2016, 04:30 PM
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You don't. There is no rifling to match, and if you don't eject a shell, there is no firing pin imprint to match either. Hell, if the victim only catches part of the pattern, it will be difficult to guess the gauge of the shotgun.

You might be able to guess the barrel length by measuring dispersal and distance from victim to shooter, but it would still be a very rough guess.

Last edited by silenus; 09-30-2016 at 04:31 PM.
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Old 09-30-2016, 04:37 PM
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OP - the real question is how reliable is any forensic bullet matching? The answer is disappointing.

http://www.americanbar.org/content/d...thcheckdam.pdf

https://thinkprogress.org/forensic-e...581#.q6gse1873

Last edited by Tired and Cranky; 09-30-2016 at 04:38 PM.
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Old 09-30-2016, 06:48 PM
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Quote:
Originally Posted by silenus View Post
You don't. There is no rifling to match, and if you don't eject a shell, there is no firing pin imprint to match either. Hell, if the victim only catches part of the pattern, it will be difficult to guess the gauge of the shotgun.

You might be able to guess the barrel length by measuring dispersal and distance from victim to shooter, but it would still be a very rough guess.
I suppose it's possible if a slug is used and there is a significant and unique defect in the barrel.
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Old 09-30-2016, 07:19 PM
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Most of today's slugs are saboted, so the only thing touching the barrel is plastic. Maybe it takes an impression better than lead would? Best in my mind would be a handloaded brass shell with no wad cup and steel shot. I'm pretty sure the steel shot would not pick up any impressions from the barrel.
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Old 09-30-2016, 08:14 PM
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[snip] ... Need answer soon-ish, I'm heading to Reno next week.
You've piqued my curiosity, what do you plan on doing in Reno next week that you don't want your shotguns traced?
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Old 09-30-2016, 08:37 PM
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One suspects that he intends to shoot a man, just to watch him die, and he wants to make sure that California's criminal justice system doesn't tie him to the crime.
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Old 09-30-2016, 10:29 PM
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One suspects that he intends to shoot a man, just to watch him die, and he wants to make sure that California's criminal justice system doesn't tie him to the crime.
The CA criminal justice folks probably won't care to much...cause it would be a Nevada case.
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Old 10-01-2016, 12:37 AM
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The CA criminal justice folks probably won't care to much...cause it would be a Nevada case.
if a resident of California shoots a man in Nevada, where are the survivors buried?








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Old 10-01-2016, 08:24 AM
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Shotgun evidence


The wad separating the shot and powder will invariably be at the scene, and should pretty easily identify the gauge. Its possible if it is a plastic wad (most are these days) and the barrel isn't perfectly smooth, it might have some identifiable marks from scratches in the barrel/choke. A step below that, the wad and shot may be identifiable to a certain lot number, especially if the manufacturer goes to the effort of marking wads.
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Old 10-01-2016, 09:46 AM
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if a resident of California shoots a man in Nevada, where are the survivors buried?
You don't bury survivors, you tie bricks to their legs and sink them in Lake Tahoe.

Last edited by watchwolf49; 10-01-2016 at 09:46 AM.
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Old 10-01-2016, 12:22 PM
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Originally Posted by GaryM View Post
Most of today's slugs are saboted, so the only thing touching the barrel is plastic. Maybe it takes an impression better than lead would? Best in my mind would be a handloaded brass shell with no wad cup and steel shot. I'm pretty sure the steel shot would not pick up any impressions from the barrel.

"Enhance, enhance." - most TV CSI type shows.
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Old 10-01-2016, 02:02 PM
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There certainly ARE ways that forensic science can provide evidence for shotgun blasts. Specifically, they can test two different shotgun pellets to see if they came from the same batch at the same factory. Tiny differences in the exact composition of the metal itself are detectable.

Suppose a woman is found dead with several shotgun pellets lodged in her torso, and upon searching her house they find a shotgun in the husband's closet, along with a half-empty box of ammunition.

#1 They can test the pellets pulled from the woman's torso to see if they are a metallurgical match to the shells still in the box.

#2 They can test the husband's hands for gunshot residue to see if he has fired a firearm recently.

#3 They can test the wife's clothing for gunshot residue to determine if the shot was fired from less than six feet away.

#4 They can test the husband's shotgun to see if it has been fired recently.

There might be more tests I haven't heard of.

Granted, it's not as good as matching lands and grooves on a bullet, but it's something. Sure, the husband's lawyer might say "My client admits that he shot at a rabbit and missed earlier that morning, and whoever shot his wife could have bought his ammunition from the same store." But if the prosecution can show motive and opportunity, forensics can certainly have the means nailed down.
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Old 10-01-2016, 02:09 PM
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Just stay away from Cal-Neva, OK? We don't need any more bizarre hypotheticals.

https://en.m.wikipedia.org/wiki/Cal_...dge_%26_Casino
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Old 10-01-2016, 04:20 PM
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There's a current discussion on Quora that just came up: https://www.quora.com/Are-shotgun-rounds-traceable
Quote:
Originally Posted by GaryM View Post
Most of today's slugs are saboted, so the only thing touching the barrel is plastic. Maybe it takes an impression better than lead would? Best in my mind would be a handloaded brass shell with no wad cup and steel shot. I'm pretty sure the steel shot would not pick up any impressions from the barrel.
Aren't most slugs rifled these days, for firing out of smoothbore? I don't think most people outside of Illinois, Indiana, etc. are using rifled barrels with sabot slugs.
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You've piqued my curiosity, what do you plan on doing in Reno next week that you don't want your shotguns traced?
Buying me a beer? But really, woosh: https://www.youtube.com/watch?v=8J7VQaWt1uQ
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Old 10-01-2016, 04:38 PM
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Crime scene techs may shoot their wad trying to id a shotgun.

I was under the impression ballistic tests from shotguns aren't conclusive evidence.

They can say at trial that a 12 gauge shotgun was used to kill the victim. A recently cleaned 12 gauge was found in the suspect's house. But they can't claim a ballistic match.

Last edited by aceplace57; 10-01-2016 at 04:40 PM.
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Old 10-01-2016, 05:38 PM
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If movies are any guide, the real injury occurs when the victim backflips twenty feet.
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Old 10-01-2016, 05:51 PM
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Quote:
Originally Posted by Sasquatch View Post
The wad separating the shot and powder will invariably be at the scene, and should pretty easily identify the gauge. Its possible if it is a plastic wad (most are these days) and the barrel isn't perfectly smooth, it might have some identifiable marks from scratches in the barrel/choke. A step below that, the wad and shot may be identifiable to a certain lot number, especially if the manufacturer goes to the effort of marking wads.
Cite?
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Old 10-01-2016, 06:34 PM
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Aren't most slugs rifled these days, for firing out of smoothbore? I don't think most people outside of Illinois, Indiana, etc. are using rifled barrels with sabot slugs.
I have both barrels for my guns. Depends where I am using them and the amount of range I want as to which I use. Sometimes I don't want the load to carry as far like when I am in more residential type areas or areas with heavy cover where I might not be able to see someone within range. Usually the smoothbore barrels for the rifled slugs are on so I can also protect the San domicile from vermin in the yard without stopping to switch barrels.
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Old 10-03-2016, 07:08 PM
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shot


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Originally Posted by Bosda Di'Chi of Tricor View Post
Cite?
I'm not sure what you want a cite for, some specific bit seem questionable, or just upholding standards? I don't think you can really cite studies that a shotgun wad doesn't evaporate, or that a scratched bore will scratch a plastic plug sliding down it at 1000 fps.

The wad/shot lot number ID is more problematic, I'm not sure any manufacturer does even mark lot numbers on wads. I've only has minimal experience with shotshell reloading, and have seen wads with numbers and symbols on them, but never checked their meaning. Even lacking that though, with forensics these days, just batch to batch differences in pellet alloy and plastic composition might be enough to provide at least a general match. That's why I said "may be" though.

This is really all from personal experience as a machinist/engineer/gunsmith, and past law enforcement experience. The LEO was decades ago though, I'm certainly behind the times with comparison tech. Of course, if you're going for academic rigor, I would have to admit that most law enforcement evidence processing and analysis is not up to science standards, and often doesn't have full foundational research support.
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Old 10-03-2016, 10:35 PM
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How does one pronounce "saboted"?
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Old 10-03-2016, 10:47 PM
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How does one pronounce "saboted"?
Well, whatever you do, don't correct William Shatner's pronunciation.
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Old 10-03-2016, 10:48 PM
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There certainly ARE ways that forensic science can provide evidence for shotgun blasts. Specifically, they can test two different shotgun pellets to see if they came from the same batch at the same factory. Tiny differences in the exact composition of the metal itself are detectable....
This is bunk.

Quote:
Originally Posted by from cited article
The composition of castings from a single pot sometimes varied, while the composition of lead in different pots sometimes matched. That meant that bullets made from two different batches of lead could wrongly appear to have come from the same pot.
In short, the chemical compositions are not like fingerprints. Well, they would be like fingerprints if your fingerprints could change during your lifetime and someone else's fingerprints could change to match yours.

A lot of forensic "science" is far from scientific. A lot of times a forensic "match" just means "we think this guy did it, well, just because".
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Old 10-04-2016, 09:20 AM
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This is bunk.

In short, the chemical compositions are not like fingerprints. Well, they would be like fingerprints if your fingerprints could change during your lifetime and someone else's fingerprints could change to match yours.

A lot of forensic "science" is far from scientific. A lot of times a forensic "match" just means "we think this guy did it, well, just because".
Thanks excavating. That's a great article and anyone who cares about criminal forensics should read it.

Interestingly, I don't know that much about whether my fingerprints can change and how likely it is that someone else's fingerprints (particularly "partial prints") match mine. The FBI fundamentally assumes that our fingerprints are unique and that they stay fixed. I haven't seen studies showing these things to be true. It's exactly those types of assumptions that the FBI lab has been making for years, without being questioned, that has led to some junk science sending people away to jail. We need to ask these questions about all the FBI's forensic science.

Here is one of my favorite paragraphs from the article:

Quote:
After retiring from the FBI in 2000, [former FBI metallurgist William] Tobin partnered with Erik Randich, a forensics consultant and metallurgist at Lawrence Livermore National Laboratory in California. The duo set out to examine whether there was any statistical basis to bullet-lead matching.
Wouldn't it have been better for Mr. Tobin to determine the scientific validity of his forensic work when he was still using it to convict people?
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Old 10-04-2016, 09:39 AM
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Thanks excavating. That's a great article and anyone who cares about criminal forensics should read it ... [snip]
It's a good read for people interested in metallurgy as well. The author does dance around a bit and run a little loose with the data, but that's understandable since there's very little scientific data available. It does seem a shame to convict people using LEO guesswork as hard evidence.
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Old 10-04-2016, 09:46 AM
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How does one pronounce "saboted"?
Good question. The dictionary doesn't list a verb form of 'sabot.' In French the pronunciation of the terminal 't' changes when you go from 'sabot' to 'sabotage,' but that's a French word following French pronunciation rules for the use of a latin-derived suffix.

My personal preference would be 'say-bowed' rather than 'say-boated.' Although I think it's weird that the first syllable of 'sabotage' is pronounced 'sah-', while the first syllable of 'sabot' (describing the expended material around a tube-launched projectile) is pronounced 'say-'.
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Old 10-04-2016, 08:15 PM
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#2 They can test the husband's hands for gunshot residue to see if he has fired a firearm recently.

#3 They can test the wife's clothing for gunshot residue to determine if the shot was fired from less than six feet away.
These ones are pretty much fantasy too.
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Old 10-04-2016, 08:57 PM
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Just strike your forensic matches on the stock, not the steel. They should light.
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Old 10-05-2016, 09:07 AM
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They Were Having a Sale at the Gunstore
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Now Roy Jukes was good at house burgling and still thought he'd escape without harm
When the owner rolled in with a shotgun
Braced on his wheelchair's arm
"Well, they'll bust you for shooting--" Roy started, but the man's shotgun cut off the lot
And he said, as he muscled Roy's corpse out the door
"There are no ballistics on shot."
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Old 10-05-2016, 11:20 AM
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Good question. The dictionary doesn't list a verb form of 'sabot.' In French the pronunciation of the terminal 't' changes when you go from 'sabot' to 'sabotage,' but that's a French word following French pronunciation rules for the use of a latin-derived suffix.

My personal preference would be 'say-bowed' rather than 'say-boated.' Although I think it's weird that the first syllable of 'sabotage' is pronounced 'sah-', while the first syllable of 'sabot' (describing the expended material around a tube-launched projectile) is pronounced 'say-'.
Actually, the noun is pronounced "Saa-boat-'tay-jee."

Cite: https://youtu.be/gMJIRTCK--I (I don't know which is weirder: that I remembered this Bugs Bunny or that the 5-seconds clip is on YouTube.
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Old 10-05-2016, 12:50 PM
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This was actually a clue in a Spider-Man comic book I read years ago. He asked a police detective about a murder committed with a shotgun, and the detective talked about finding a forensic match to another murder, or something like that. A few issues later,

SPOILER:
Spider-Man figured out the detective was the killer with other clues, and is angry at himself for not remembering that it was impossible to do forensic matches on shotguns. The villain called himself Sin-Eater, by the way.
  #32  
Old 10-05-2016, 07:13 PM
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Wouldn't it have been better for Mr. Tobin to determine the scientific validity of his forensic work when he was still using it to convict people?
As a current government employee, I'll say that performing tasks on the job that aren't part of your job duties can lead to ethics violations and any number of potential forms of discipline, and also doing things that reflect poorly on your agency is bad for your career.

It's almost tradition to do stuff that undermines your former employer once you leave government employment, though.
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