Can you trace bullets like fingerprints?

[beautress]

Can someone explain it to me how the police can trace bullets like fingerprints? And can you do it without the actual gun? Reason I'm asking is b/c in No Country For Old Men, lewelyn has a rifle and he's t he g ood guy,kinda. So why would he have a rifle to fight the bad guys when it could trace back to him? Many movies are like this.

Here ya go, arnieisblack:
​

 

[whitehall]

If he has the weapon, a skilled ballistics investigator can make a comparison between a fired slug found at the scene of a crime and a freshly fired bullet. The lands and grooves have distinct markings from minute imperfections in every barrel. It's not just the marks but the relationship to each other in the comparison like fingerprints. A ballistic investigator can also determine what kind of weapon based to the dimensions of the lands and grooves and the twist in the rifling. firing pin marks in an expended cartridge can also be compared with reasonable accuracy.

 

[Jarlaxle]

It's not real. Ballistic "fingerprints" are a fantasy. Identify a caliber, sure. Rule OUT a gun, maybe. Identify a model of pistol...possibly. (Offhand, Colt and Smith and Wesson use different rifling.) Identify a specific gun? No.

 

[WinterBorn]

Dang! I was going to ask if you could get me Columbo's autograph.

If you want Columbo's autograph, you need a Medium, not a detective.

 

[whitehall]

It's not real. Ballistic "fingerprints" are a fantasy. Identify a caliber, sure. Rule OUT a gun, maybe. Identify a model of pistol...possibly. (Offhand, Colt and Smith and Wesson use different rifling.) Identify a specific gun? No.

Don't take up a life of crime if you think ballistics is a fantasy. While there apparently is no data base of firearms, it's easy for a ballistics expert to make a comparison if he has the weapon and the fired bullet. Firing pin impressions in a shotgun shell. The rate of twist on a fired bullet. They are all part of ballistic evidence.

 

[Jarlaxle]

Don't take up a life of crime if you think ballistics is a fantasy. While there apparently is no data base of firearms, it's easy for a ballistics expert to make a comparison if he has the weapon and the fired bullet. Firing pin impressions in a shotgun shell. The rate of twist on a fired bullet. They are all part of ballistic evidence.

CSI is not real. The rifling marks on my wife's pistol are identical to the previous 50 and next 50 barrels on the line. (Source: gunsmith who has testified in Federal court as an expert witness.) My S&W Model 29 is on at least its third barrel, and I suspect the markings now are different from the markings when the barrel was new. CSI is TV, not reality.

I will give you a trillion dollars if you can compare rifling marks from a round from my uncle's target rifle to anything. (The rounds from it-spinning 500,000+RPM and traveling ~4000fps-disintegrate on impact.)

 

[whitehall]

CSI is not real. The rifling marks on my wife's pistol are identical to the previous 50 and next 50 barrels on the line. (Source: gunsmith who has testified in Federal court as an expert witness.) My S&W Model 29 is on at least its third barrel, and I suspect the markings now are different from the markings when the barrel was new. CSI is TV, not reality.

I will give you a trillion dollars if you can compare rifling marks from a round from my uncle's target rifle to anything. (The rounds from it-spinning 500,000+RPM and traveling ~4000fps-disintegrate on impact.)

The science of ballistics is real and verified in a hundred years of court cases. Some rounds disintegrate on impact and aren't suitable for ballistic comparison but they can sometimes reveal the caliber and sometimes the vintage of the round based on the chemical composition and weight. I worked with a ballistic expert years ago and I can promise you that they can match up an individual slug from a weapon that seems identical to a thousand others. Every weapon that has been fired leaves traces of deposits in the barrel and each of these deposits leaves a minute mark on the recovered bullet that can be compared to a fresh round from the weapon.

 

[Jarlaxle]

The science of ballistics is real and verified in a hundred years of court cases. Some rounds disintegrate on impact and aren't suitable for ballistic comparison but they can sometimes reveal the caliber and sometimes the vintage of the round based on the chemical composition and weight. I worked with a ballistic expert years ago and I can promise you that they can match up an individual slug from a weapon that seems identical to a thousand others. Every weapon that has been fired leaves traces of deposits in the barrel and each of these deposits leaves a minute mark on the recovered bullet that can be compared to a fresh round from the weapon.

If I fired a round from my Model 29, ran a steel file through the barrel, and fired another round, the rifling would not match. (Even if the rounds remained intact, which they usually do not.) Most rifle rounds fragment on impact. Rounds from my uncle's target rifle don't fragment-they disintegrate, to the point I doubt even the CALIBER could be determined with any certainty. (Like most high-velocity rifles firing lead rounds.)

Bite mark analysis was "verified" in many cases...until it was shown to be mostly bullshit.

 

[whitehall]

If I fired a round from my Model 29, ran a steel file through the barrel, and fired another round, the rifling would not match. (Even if the rounds remained intact, which they usually do not.) Most rifle rounds fragment on impact. Rounds from my uncle's target rifle don't fragment-they disintegrate, to the point I doubt even the CALIBER could be determined with any certainty. (Like most high-velocity rifles firing lead rounds.)

Bite mark analysis was "verified" in many cases...until it was shown to be mostly bullshit.

You can deface all your firearms with files and metal rods but it would make the next round fired from an altered barrel easier to match with a fired slug.

 

[JohnDB]

Most people who commit assault crimes using guns aren't exactly the brightest bulbs on the tree.

Currently, those who own firearms are usually watching out for the BATF and trying to avoid their attention. Many of your gun enthusiasts are machinists in training. Files, drills, bores and etc can change the "signature" of any firearm that possibly got left on any round or cartridge the firearm came into contact with.

You can change everything from a receiver characteristics to a firing pin pattern and Barrel in a matter of minutes. It isn't difficult or labor intensive. Guns aren't rocket science by any stretch of the imagination.

Guns aren't magic...they aren't unchangeable or difficult to modify.

However, for the ne'er-do-wells of our society they haven't got a clue how to do any of these things. They usually keep their guns AFTER committing serious assault crimes in locations that lead police straight back to themselves. (If the police detectives bother themselves that much)

Most crimes are committed by using stolen guns to begin with...meaning they already committed a crime by stealing the firearm instead of legally obtaining it.

 

[Bob Blaylock]

As I understand it, from being a TV detective, they can match 2 bullets by the rifling marks they leave on the bullets. That way they can tell the bullets came from the same gun but, without the gun they can't trace those bullets back to the gun that fired them. Unless there is some 'rifling' data base I don't know about. Criminals use stolen guns that can't be traced to them typically.

My understanding is that that's not at all reliable, if enough bullets have been fired from the same gun, between the two that are being matched. Every bullet wears the bore, and changes the pattern of scratches and marks that that barrel leaves on subsequent bullets. Perhaps even some corrosion effects as well.

If two bullets are found at the same crime scene, I think they can reliably determine if they were fired from the same gun.

If they get their hands on a gun that they suspect to have been used in a crime years ago, but which has since been fired enough times since then, I do not think that they can match it with a bullet from that crime scene.

 

[Bob Blaylock]

Most guns will have a spent casing included in the case to show that a round has been fired and the rifling marks recorded.

Depending, I suppose, on the precision and consistency with which they are manufactured, I would expect that any brand-new gun would be an almost exact ballistic match for every other brand new gun of that same make and model. Perhaps even with other models that use the same barrel.

I wouldn't expect any gun to develop any unique, identifiable “fingerprint”, until enough bullets have been fired through it to wear it in some way different than how other similar guns have been worn.

 

[Leo123]

My understanding is that that's not at all reliable, if enough bullets have been fired from the same gun, between the two that are being matched. Every bullet wears the bore, and changes the pattern of scratches and marks that that barrel leaves on subsequent bullets. Perhaps even some corrosion effects as well.

If two bullets are found at the same crime scene, I think they can reliably determine if they were fired from the same gun.

If they get their hands on a gun that they suspect to have been used in a crime years ago, but which has since been fired enough times since then, I do not think that they can match it with a bullet from that crime scene.

Good points. Eventually, after many firings, the lans and grooves could change. At that point the person evaluating the bullets and their experience would have to come into play and the final decision would be up to a jury. Besides, lans and grooves in bullets would just be one part of Prosecution discovery. If lans and grooves were the ONLY evidence it could get complicated and harder to prove.