What Degree of Specificity Can a Fired Bullet Reveal the Make and Model of the Gun it Came From?

[Shanvanvocht]

As far back as 1934, in his book "The Identification of Firearms and Forensic Ballistics". Major Sir Gerald Burrard cautioned that barrel wear from firing even lead bullets would substantially alter individual characteristics. making a match difficult if not impossible.

 

[golden]

An article in SCIENTIFIC AMERICAN questioned whether tool marks examiners are correct when they claim a bullet is a match or not. While it has been claimed that every barrel is unique, them may not be unique enough. It has gotten so controversial, an FBI examiner has been coaching forensic technicians to argue in court that questioning there claims, would be tantamount to making them lie or perjure themselves in court.
That worried me when I read it.
I can see how you can claim a bullett came from say a COLT and not a SMITH & WESSON because of the rifling or that a bullet is the same caliber, but you would need a unique mark from say damage to the muzzle or forcing cone or have a unique design of barrel to claim an individual gun fired a certain bullet.

This may have an effect of court proceedings if it is brought up for dispute or appeal.

JIm

 

[rust collector]

The trouble with experts is that they are human, and therefore tend to lose sight of their own fallibility. One attorney invites them to extrapolate, while counsel on the other side of the issue wonders how they got so far past the point supported by objective measurement. That is why scientists don't get to decide the ultimate facts. Recommended reading: https://www.smithsonianmag.com/science-nature/myth-fingerprints-180971640/

 

[Slamfire]

I listened to a program about the failures of finger print identification, not to get into the failures, but rather what caused a few. Finger prints collected at a scene are seldom 100% perfect and 100% complete. If they were, then matching a fingerprint to a person would be very certain. The problem is, when a finger print is smudged, somewhat obliterated, and partial, then the examiner is trying to match with partial information. And it turns out, humans using partial information are subjective in their judgement. And unreliable.

So if the bullets and cases were 100% perfect and 100% complete that ought to provide a "good" match. What about a case that has been walked on, dented, etc? Something else I remember reading, is that modern machining has made firearm lots identical for all participial purposes. So the case out of one firearm could match all of the production of that firearm.

Older firearms probably do have the classic tooling marks that Hatcher wrote about in his Text of Pistols and Revolvers, published 1935. But since CNC, nope.

 

[GooseGestapo]

Alternatively, you can have a Known weapon (Chinese Norinco SKS), cartridge cases, unfired ammo, fired projectiles recovered from a victim, and evidence techs unable to match them….
Had a case where a subject shot a doe, bullet (Russian 7.62x39 FMJ) penetrated the deer… ricocheted off a flat rock outcropping, hit a nearby mobile home door, penetrated the door and hit an elderly woman in the knee sending her to the ER. TopHats x-ray reminded me.

I got a conviction nevertheless. Criminal recklessness with a firearm. Convicted felon with a firearm and related game and fish charges.
He got the hunter biden treatment! 5yrs probation, fines, restitution (of course never paid…) and credit for time served prior to court….

 

[Jim Watson]

Here is that Scientific American article. It is not at all favorable to the notion of matching rifling engraving on bullets or tool marks on brass.
https://www.scientificamerican.com/article/the-field-of-firearms-forensics-is-flawed/

 

[CapnMac]

And a court decision in MD basically says that, under the law, there's not enough specificity to convict.

 

[JohnKSa]

What it says is that an expert witness may not state that a "ballistics match" is absolute to one specific firearm to the exclusion of all others. They can only state that it there is a match that indicates the bullet is consistent with having been fired from the gun in question (but not to the exclusion of all others), or that it was not.

That does mean that a ballistics match, in the absence of any other evidence at all probably isn't going to be enough for a conviction, but in other circumstances could certainly provide evidence that contributes to eliminating reasonable doubt.

Of course, using rifling and bullet characteristics to determine make model is quite a bit different since there's no attempt in that case to match to a specific weapon in the first place. It's only going to narrow things down (at best) to a particular make/model and perhaps (if one is really lucky) a range of manufacture dates.

 

[Zahn]

Hollywood is tainting the jury pool with their TV shows, where they show police and CSI techs using a comparator scope, and our 'hero' says, "got him! Perfect match!" And if the defense and defendant don't know to challenge it, a lot of bad evidence is used at trial.

 

[Jim Watson]

Yes, when an expert witness says “consistent”, Joe and Jane Jurymen hear “he did it.”

 

[UncleEd]

I know little to nothing about this subject other than the rifle
authorities have in the killing of Martin Luther King tends
to give different results in tests over many years. The
conviction in the case was not based on the rifle/ballistic match.

And a police detective sergeant once told me that if an expert gives
a report on a bullet, a defendant can find another expert to
challenge him.