So can you tell if a Shotgun was the one used in a crime..

I always figured that a shot cup should be fairly easy to match to a shotgun barrel... .

How would that happen? assuming we are talking about a smooth bore? Your best bet would be if you recover the fired shells you might be able to identify the shotgun from unique marks that might be left from the bolt face, firing-pin, extractor or ejectors. A smooth bore shotgun is unlikely to leave unique marking on the shot cup assuming there was no damage to the barrel or choke

In general even with bullets and regular center fire cartridges these forensic techniques don't work all the time or even most of the time. They are even more rare to become pivotal in an actual court case. It the entire 15 year lifespan of Maryland's ballistic finger print database (those fired cases you use to get with a new handgun purchase) the data collected was NEVER the critical evidence that a conviction pivoted on. It was IIRC only used in one or two cases and was not critical to the conviction.

milemaker13 said:

Almost seems like it would be easier to positively rule a shot gun out vs prove it is the actual murder weapon.

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That is the premise in the OP...”proved not to be the gun used...”

Smooth bores aren't really smooth, especially those that are cut off, have dinged muzzles, corroded bores or chokes.
Matching these irregularities to a fired shot cup sounds quite feasible to me.

I've always wondered about this myself. I got cold feet typing in to Google "can a shotgun get traced back to someone if they murder someone with said shotgun". Seems...suspect

Gunny, that's incredible. The hull has a lot to say apparently. But like others have suggested, if you pick up the hulls, the murder weapon now becomes untraceable and you can go back to duck hunting?

indy1919a4 said:

Was rewatching the crime drama "Laura" the other night. Basic story a lady is shot with a load of buckshot and murdered with a shotgun. Later the police detective announced that they had proved that the shotgun owned by one of the suspects was tested and proved not to be the shotgun used.

Is that possible?? I can understand a bullet shot from a rifled barrel being proved it came from a certain gun but can buckshot be proved not to come from a certian shotgun.

Click to expand...

As @Odd Job and @GunnyUSMC said, there's quite a bit more to forensics when it comes to firearms than the stereotypical bullet riflings we're all familiar with through the various media and entertainment sources.

There's metallurgy, chemistry, X-ray (radiography) analysis, ballistics, math, and more. Heck, there's probably some poetry in there as well.

Let's take a bullet from a pistol or rifle, for example.

Let's start with the rifling marks on the bullet. Without even having the firearm the bullet came from to "match" specific marks to the specific rifling, it may also be possible to identify the type of firearm the bullet was fired from, possibly even the make/model. As one very clear example, Glock barrels do NOT have rifling like any other manufacturer. So a bullet of known caliber with Glock rifling markings automatically narrows the potential firearms down to a handful of Glock models. The number, width, and direction of twist in the lands/grooves says a lot.

How specific can these rifling markings be? Well, without actually having the exact firearm used to examine, they can be specific enough to determine a make and model (see the example above), and even where and when the firearm was manufactured. For example, if they determine by the markings that the firearm came from a certain manufacturer, they may also be able to determine by the markings that the barrel rifling was made during a certain time when a series of barrels were made with a certain cutting die which had a minor defect that was not noticed by the company's QA people until after a certain number of barrels were manufactured.

Not only are there rifling markings on the bullet, there are also chemical residues from the primer/powder that was used in the cartridge that fired it. Chemical analysis may produce results which could help determine who manufactured the ammunition that was used.

There are also physical characteristics inherent with the bullet design, materials, and construction which may identify who manufactured the bullet. Speer Gold Dot hollow points are distinct from those manufactured/used in Hornady, Winchester, Federal, and Sig Sauer ammunition.

On a metallurgical level, there may be trace amounts of metals/alloys from the firearm the bullet was fired from, and on the flip side there most certainly will be trace amounts of the bullet metals/alloys present in the barrel of the firearm which shot it. This can extend right down to the crystaline structure of the metals/alloys found. If anything about these trace metals/alloys can be shown to be unique to the bullets or the firearm in question, even if only down to the particular make/model of the weapon if not specifically to one, then you've established a connection.

Fired cases also retain physical markings other than the obvious manufacturer markings on the base. Firing pin markings on the primer and chamber markings on the sides of the case to name a couple. On a chemical and microscopic level, there may also be trace amounts of metals/alloys from the firearm itself.

Ejected cases retain some evidence of the ejection mechanism and action markings, not to mention markings inherent with stacked ammunition in magazines, which may further identify the firearm type. For example, bolt action, lever action, semi-automatic, etc.

While I used the example of a rifled bullet, there are many, many other forensic tools to be used which are perfectly adaptable to any firearm related evidence, even shotguns.

As an engineer, I would have to say that knowing what something ISN'T is just as important as knowing what something IS when trying to make a connection between bullets/pellets and firearms.

Here's a link to something I read up on about this a few years ago, when I was looking into firearms forensics:

https://www.nist.gov/system/files/documents/forensics/Firearms_identity_NDAAsm.pdf

There are three main areas used when matching cartridge cases and shot shells, the breach face markings left on the primer, the chamber marks on the outside of the case or hull and the ejector mark.
If they have cartridge cases or shotgun shells from a crime scene, they are inspected and entered into NIBIN and checked against the database to see if they they match any other crimes. This only checks the breach face and ejector marks. If a match is made by NIBIN , the cartridge cases from the matching crime are submitted along with the current shooting case to be microscopically compared. This is where all the other markings are looked at.
Now if there’s a suspected gun, that gun is test fired with three or more rounds of ammunition. These are then compared to each other. These are referred to as KNOWN. The examiner knows that they were fired from the gun. Once they have matched them, they are compared to the evidence.
When I started doing NIBIN back in 2012, I found that most of the examiners could look at a cartridge case and identify Glock and Hipoint. This is because they have very distinct subclass breach face markings.
I was lucky that I was the only one on my department that testified the evidence guns. I started paying attention to the different types of markings and after a couple of years I could identify several guns just by the breach face markings.
The Gen5 Glock breach face markings are totally different from the previous Gens. The Springfield XDS had an odd rectangular firing pin strike with a drag mark on the side. After Springfield discovered that they could not fix the issues they were having with the XDS going off when the slide went forward, they redesigned The striker system and now it looks close to a pre Gen5 Glock.
Bullets can be matched to a gun by the number of lands and groves and the direction of the twist. Now there are some that fall into groups that have the same number and twist so you can’t always go by that. But it is often used to eliminate.
Glock changed it rifeling on Gen4 gun which made it easer to match up bullets, Gen1 through 3 were almost impossible to match. The new Gen5 barrels are much easier to match.
There are a lot of things that are not talked about outside of the firearms forensic field, have to have those tread secrets to stay ahead of the bad guys.

I’ve read it’s almost impossible to match a bullet to a handgun if the barrel has polygonal rifling. Any truth to that?

I was told about a case when the shotgun wasn't even recovered by the police. There were one or more expended shells at the scene. The bad guy was found to be in possession of expended shells and live shells that had been cycled out of the shotgun. So he tossed the gun into a lake or whatever he did with it, but probably saved shells he pumped out of it at some point and probably left some he fired at cans or critters or whatever on his property.

if found under the perp in a home invasion that was shot by the home owner. just kidding.

Interesting information, thank goodness criminals are dumb and examiners are sharp.

Just because we catch the dummies doesn’t mean that everyone breaking bad is stupid... Something to think about.