Guns and bullets are used in the most serious crimes, and they also happen to leave the most damning evidence.

While it’s often obvious when initially walking into a crime scene whether a gun was used – even if the victim survived and is being treated by paramedics – a full examination of the scene is always required to look at all factors that impacted the event. When a gun is involved, however, crime scene investigators will look for specific clues such as bullet casings, bullet holes, spatter patterns, and perhaps even a dropped weapon – either at the scene or nearby, such as in a body of water or a dumpster.

After the scene is photographed, diagrammed and all evidence referenced, the shell casings, bullet fragments, weapons and other evidence can be gathered, preserved and catalogued for further study back at the lab. Bullets suspected to be drilled into soft plaster or furniture will not be pried out. The area around and containing the bullet will be cut out so that the bullet can be removed carefully at the lab, and thereby preserve the channel that the bullet made.

 

1. Striations on a fired bullet

Once a bullet is recovered, either from an impact point in a soft wall or pulled out of flesh by a medical examiner or a physician, that bullet will become a primary piece of evidence. Every gun barrel is rifled during manufacture, or finished inside the barrel with rotating grooves to impart spin to a bullet in order to improve accuracy during flight. The resulting spiralling grooves and lands (the flat parts between the grooves) leave mirrored markings on the bullet itself.

If you are able to fire another bullet from the same gun, an investigator can match the grooves under a special microscope which displays both bullets side by side, comparing the strata. Since there are several processes involved in rifling a barrel, each barrel is unique. Just like fingerprints, a bullet can be paired to a weapon with nearly perfect accuracy.

Further, even without a weapon, the striations can identify a type and model of firearm, so detectives will know what to look for.

 

2. Gunpowder residue leaves expected patterns

When a gun is fired, the bullet is not the only thing that comes out of the barrel. Burning powder particles also expectorate and will create a pattern on the object closest to the barrel. This pattern varies by how far the weapon is from the target. By knowing the patterns of a particular firearm, a consensus can be reached about how close or how far away the gun was. If there are no powder marks on the hand holding the gun or the forehead around the bullet hole, it is unlikely that the victim shot himself, so suicide can be ruled out no matter how convincing the pose looks to the untrained eye.

 

3. Trajectory, ricochet and bullet holes

Sticks carefully inserted in bullet holes can indicate direction of the bullet, and, if many holes are found in a scene, these sticks can help triangulate: where the shooter was standing; how tall he (or she) might have been; and many more details. Bullets that ricochet will collect trace evidence from where they bounce, and add further detail for the investigator.

 

4. Hidden fingerprints

A gunman will finger bullets as he loads them into a cylinder or magazine, and leave tiny quantities of salty sweat with each touch. When a bullet is fired away from its casing, tremendous heat is instantly transferred to that metal, vaporising the moisture and setting the salts from those prints. The salts become molten and a chemical reaction with the metal etches the fingerprints permanently into the casing.

 

5. Firing pin impressions

Firing pins leave individual marks on the primer (the explosive cap that ignites the gunpowder when struck by the pin on the tip of the hammer) at the very bottom of each bullet. The alignment, size of impression, and age of the firearm also contribute to individualised marks as the hard metal (the pin) make impressions on the soft metal (the primer).

 

6. Bullet damage to tissue

Wounds can provide an incredible amount of information about sequence of hits, distance, velocity, bullet type, caliber, and more – whether a bullet fragment is recovered or not. Bevelling around an entrance wound holds clues, fracture lines in dense bone such as skulls can identify distance, velocity and direction of fire. Grazing bullets leave skin tags – little flags of ragged skin that are pulled up and torn as a projectile passes by at high speed. All of these indications help validate the opinions of a medical examiner.

Every one of these indicators can become a comprehensive study in itself. While we only have room for a highlight from each factor, there have been: books written about each subject; experts have spent decades studying only trajectory, for example; and hundreds of thousands of tests repeated over and over again verify the science and validate the findings.

Your Turn: Do you think a bullet fired from a gun can be matched to that gun a decade later, after it has fired thousands of additional rounds? Sound off in the comments below.

Comments

comments

23 Responses

  1. Shanagaye Spence

    Yes I think a bullet fired from a gun can be matched to it decades later because of the forensics scientist (ballistics) will compare the bullet to a specific firearm to see it match a certain caliber of a gun. It is then examined for the determination of the rifling impressions on the bullet if it matches the barrel in question. If these class characteristics are the same he then try to make a positive identification between the traits that have being transferred from the barrel gun to the bullet.

    Reply
    • Douglas Filter

      Shanagaye, you are absolutely right – with some caveats … as we reported in Number 1, above. However, what if the gun is never recovered? What if the gun has had a new barrel affixed (on some automatics, rifles, etc, this is possible). What if the gun barrel has been redrilled and the striata changed? What if the gun has been laying in the sea – in salt water for ten or more years? Rust, salt, caustic chemicals … many different things can work against making a positive identification.

      Wear and tear on a gun can also alter the identifying striata as each bullet fired leaves something in the barrel from the metal itself being directed on a path set by the rotating grooves in the barrel. A gun that has fired tens of thousands of rounds over a decade, especially if that barrel is not cleaned regularly – will leave different marks on the bullet from the first to the ten thousandth.

      What about the bullet itself? If left to corrode, if ricocheted, if broken into bits upon impact with bone or something harder than the bullet itself – may not show the stripling necessary to match to a particular barrel.

      In a perfect world, the marks on a bullet will always match up to the barrel that expelled it. But in crime and forensics, there is always the extraordinary condition that presents challenges.

      Reply
  2. Suline van der Merwe

    Wouldn’t it be easy for criminals, with the basic knowledge of guns, to scratch the inside of the gun’s barrel to change the future striations on the bullets? Is there a method to prove without a doubt that the gun is the same gun used committing the crime in court if the striations don’t match precisely? Also, is it possible for gun manufacturers to manufacture guns in such a way that changing the striations would be nearly impossible? I believe that if certain factors, such as the material used in the barrel, are perfected to some extent that the striations couldn’t be altered after manufacture and that it could be used to match the gun a decade later. Currently there are too many factors that could impede the match and hopefully they could be changed with modern technology. u15180965

    Reply
    • Douglas Filter

      Hello Suline – It would be impossible to make scratches look anything like striata, especially if one is cutting them in from the front of a gun barrel and not able to effect the barrel closer to the chamber. When fired, yes, different marks would appear, but these would be suspicious in their own right because they would obviously be unnatural. Just like scratching off a serial number, damaging the evidence could, if done with enough force, obscure the striata (or numbers), but at the microscopic level there may still be some matches. One other thing, once a barrel has been deformed or defaced, it would not be a good idea to fire it again.

      Reply
  3. PGHGirl

    I have a question ( I’m not very good at these types of things yet have been curious since getting my conceal permit years ago.
    With all of the thugs, trigger happy, and just down right fools out in the world today ,along with the career criminals who have ( or feel they have to ) to go above and beyond to learn these tricks of the “trade” to NOT get caught …
    How would a police officer/forensics personnel NOT have something in place that would just implement that particular bullet to the owner no matter where in the world they would be ( in state or out of state crime) . and for gods sake, why are there not better laws in place for gun owners…… Just because you can own one , doesn’t mean you should – example, I went to the gun store and picked up my 1st hand gun ( I do in fact have a permit to carry and have also taken a 3 hour training given by state patrol) but that doesn’t take away from the fact that I went in, and in 25min I was home with my new gun. something there should change … maybe a 3-7 day hold where the state can really KNOW who they are allowing a purchase vs, maybe something hidden away in old files come to light and they shouldn’t own one but now it’s too late .
    sorry this was a bit winded and yes here it’s late so there is also a few mistakes with punctuation and spelling so I’ll apologize in advance.
    Thank you
    BE SAFE

    Reply
    • The Forensic Outreach Team

      Thanks for your question.

      If we understand you correctly, you’re asking why there are no standard mechanisms in place already to match a bullet to a specific gun. Unfortunately, we don’t have the answer to that — but there have been attempts at regulating this in various ways (e.g. bullet serial numbers, fingerprinting owners for authentication before purchases). We imagine quite a lot of this has to do with the politics surrounding gun ownership.

      Reply
      • Eric Nemo

        All weapons must be registered to the owner in the jurisdiction where I live and be bench fired with the lands and groves recorded with the police.

    • Sonny

      There is a 3 day wait when you don’t have your ccw…having your ccw means you have already gone through the screening. That is why you could bring your gun home the same day. The police who gave you your 3 hr course should have told you that. But you can’t expect the police to know the law.

      Reply
  4. Dona General

    Yesterday I saw a TV report about a young man who, through open resource software and a 3D printer, produced a resin based rifle that works! Would the same forensics evidence apply to this weapon?

    Reply
    • The Forensic Outreach Team

      Hi Dona —

      This has to be one of the best questions we’ve been asked, and is possibly inspiration for another article. The answer is: it depends. Not unsurprisingly, the reality of 3D printed firearms has caused a lot of uproar since they cannot be traced using some of the above techniques. They lack serial numbers or central manufacturing. In addition, ballistics testing wouldn’t be effective, as the barrel and pin of a 3D printed gun can be replaced easily.

      Others, however, have argued that creating a gun in this way isn’t exactly easy. They also tend to be difficult to actually use. Finally, you cannot 3D print bullets — and these, say some, should be the targets of regulation in the future for this exact reason.

      Hope this offered some insight!

      Reply
  5. Joeg Voll

    This is a very good, well written, informative article. I found it when I Googled “Can a shell casing be traced to a particular gun?”. I was watching The First 48, a homicide investigation show on A&E, and I became curious. You answered my question and then some! Thank You!!! xxJV

    Reply
  6. Gman

    Take the guns away …so then more pipe bombs and stabbings and criminals will always get guns if they want one……whi cant drive to the ghetto and buy crack or heroin ? Prohibition dies Not work it never has in human history. What does work best is plain kindness. In General stop treating people like crap pay fair wages and half the crime will disappear

    Reply
  7. John

    Can DNA be found on a fired bullet? I heard heat damages DNA, so therefor I would think if the bullet was a thru and thru fired shot the DNA would be no good.

    Reply
  8. Cisco

    I found this article while trying to find an answer to a nagging question. I am retired military and have experience identifying weapon type, caliber and range of indirect weapons. The question I can seem to answer is how range is determined with small arms. I really enjoyed reading your article and found the information interesting. Can you advise where I could find the answer to my range question? I know how it is done when the shot is heard or seen, also using a gunshot location system; however, can it be done just from the bullet, wound or impact? Thank you in advance.

    Reply
  9. lucy

    How can we tell the bullet caliber used and distance from the shot by the woundon the body?

    Reply
  10. Aesop

    This is a cool article. i’m doing a school project on forensics and this helped a lot. THANKS!!!!!!!!

    Reply
  11. Imke Jansen-Munday

    I have a rather convoluted question which I have a feeling will be unanswerable, but I could be wrong. I’m curious as to whether a hole in a wooden shield that is from roughly 1770 would still contain viable evidence suggest ballistic damage? This question is in relation to the shield featured on the website below:

    http://www.britishmuseum.org/research/collection_online/collection_object_details/collection_image_gallery.aspx?partid=1&assetid=602472001&objectid=490919

    The reason I ask this, is for the questionable acquisition of said shield by members of the Endeavour, the ship which ‘found’ Botany Bay and current day Sydney, Australia. I’m trying to come up with physical evidence to suggest malicious intention based on the characteristics of the hole. The shield has been subject to some analysis, however I get the feeling from the description of this that they are trying to avoid attributing said hole to a gunshot. Instead it has said to be caused by a ‘lance’, due to accounts from Joseph Banks journal. If so, would this show differently, when compared to musket shot holes?

    Reply
    • Bill Gray

      Lead residue in the hole would be a strong indicator it was not a lance

      Reply
  12. ngcobo

    I was on duty when robbers rob one of kfc store is fire two round and firearm was taken so want to know how long firearm take at forensic test to be done

    Reply
  13. Cat

    If a single casing is found at a crime scene and then at another location out of 600 shells beimg dug up. (These have been in the groumd for like 6 to 10 yrs.) Two of the casings are identical matches. Keep in mind theres no gun to compare to. My question is: is it possible to have identical matches with that much time inbetween firing. I would think that as the gun is used eventually over time the groves made on the casing would change.

    Reply

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