Ballisitic Testing/Matching

S

Sevens

New member
I saw in a discussion elsewhere about the idea of buying a different barrel for a semi-auto in the event that someone got shot... swap the barrel out and now the shooter is "good to go" with no ballistic match on the bullet fished out of the victim.

If you get all your info from TV and movies (as so many of us do! :o ) you have learned that they can ballistically match bullets to guns/barrels in a crime lab.

My question is, are they matching a bullet to a particular brand/style/caliber of gun, or a single, specific barrel?

What I'm wondering is... Let's say you go to the gun store and check the display case for the Springfield XDs and you find two of them, but compacts, same features, same barrel length, same caliber, and consecutive serial numbers -- so that these pistols are as much the same as the factory would typically make two from the same line.

Then you fired both of them 200 times and with the last shot of pistol A, you captured the slug and then took both pistol A & B and the single slug to the world's best crime lab...

Could they match the bullet to "a 4-inch barreled 9mm, likely an XD Compact" or could they realistically match that bullet to pistol A specifically, and not just to any XD Compact 9mm in that serial number range?

In my mind, it seems to me that every single barrel and chamber that ever leaves the Croatian assembly plant where it's forged would have to be somewhat different, however slight, for some crime lab to be able to sincerely match a bullet to a specific barrel.

Or, let me put the test in a different way: Say you get 100 XD pistols, all 9mm compacts, all the same features, 100 of them with consecutive serial numbers. You give each of them a 200 round break-in with the same ammo and then you take 100 rounds of equal ammunition, also from the same production lot. You shoot one more round through each pistol, collect every bullet, and then take the entire 100 slugs and 100 pistols to the world's best crime lab...

And the lab is stocked with endless equipment, staffing, time and money to carry out the project.

Could you match each bullet to each pistol and be correct? Could you even be 95% correct?

I mean, you look at a finger print on your hand and look at a finger print on someone else's hand and you can see the almost infinite combinations present. But a gun barrel, from a production line, where they make tens of THOUSANDS of them, one after another at high speed?

Are each and every barrel different enough to put a scar on a bullet that can be traced to one single barrel?!
 
This is an excellent question, I don't have any of the answers, but I am curious in following the thread, could raise an interesting topic of conversation.
 
I would say they will match the bullet to the very barrel. No two barrels will ever produce the Exact markings, even two barrels made one after the other.
They can sometimes reference a pattern (lands, #grooves, right/left twist) to a certain mfg and probably model(depending on how many models use that barrel).But if you bought a replacement barrel(and didn't have a paper trail to that barrel)they could not proove that the bullet was shot out your gun.
 
I would expect the breechface and extractor also leave identifying marks. I would also suspect that picking up brass and changing barrels would likely be construed as evidence of knowledge of guilt. Last, I would expect this thread to get locked very, very soon for advocating illegal or unethical behavior.
 
While it's quite possible that it gets locked, I'll be sure to post right now that it is certainly NOT my intention to even suggest such behavior.

I'm just really wondering about the nitty gritty of ballistic testing. I just can't see how a barrel maker can make EVERY barrel different when they made hundreds/thousands daily on equipment that turns them out like they are making widgets.

A finger print, now that's complexity. A 4-inch rifled barrel? How many different ways can they possibly make one?!
 
Sevens, it's got more to do with imperfections than processes, or at least that's what I would assume. Two barrels, made at the same plant, may have small but identifiable differences due to the way a tool made initial contact, or due to age and wear on a bit that made one of the barrels.

One barrel may have a slight burr in one or more grooves, for instance.

Kind of like a knife might be matched by a small notch in the blade, that affects the way it cuts.

Still, I think that switching out barrels would be a very, very bad idea if one were ever involved in a shooting, and think if we want to discuss this kind of thing just for the science of it, or because some of us may be working on some story-writing, we should make very clear that any appearance of attempts to alter evidence could backfire in a massive way.
 
Tool Mark Analysis, which can also include examination of bullets and shell casings, is a science, but it is not an EXACT science.

It's not often that an examiner can say, without a doubt, that X bullet or X casing was fired in Y gun.

The condition of the bullet or casing, especially the bullet and what it hit, can dramatically affect the examination process and can really screw up the possibilities of a match.
 
While it may not be an exact science, it can often give a good idea, and can sway a jury. Defense experts would argue the inexact nature of the science involved, which could sway the jury the other way. Ideally, the prosecution's case would not rely solely on bullet or casing analysis.

However, picking up the brass or swapping the barrel of a gun would look very suspicious, should the police ever track down the shooter by other means.

So, could switching barrels help? Maybe. Could it hurt? Definitely. Appearances matter in any trial.
 
"While it may not be an exact science, it can often give a good idea, and can sway a jury."

Yes, and I never intended to indicate otherwise. Fingerprint analysis is also far from an exact science, yet it's used routinely.

Toolmark analysis has been around for a LONG time.

Part of the prosecution's evidence in the Lindburg Baby case against Bruno Hauptmann rested on saw marks in wood of the ladder that was used in the kidnapping.
 
As I have no idea how ballistic testing is done I can say that every time a piece of metal touches a tool bit on conventional machines or cnc that it dulls and changes ever so slightly ..hence the need for quality control..and when the bit changes im sure there is the slightest difference between the two pieces made..however I do not know how significant that difference is...I do know that there is one
 
Take it to the next step and change out the firing pin also. Unless we have a working or retired expert in the field to comment on the intricacies of ballistic testing all else is speculation as good willed as the comments are/will be.
 
There's some very good articles on all kinds of investigation and forensics topics on the web, for mystery writers.
Makes sense, though.
Do a search for forensics for mystery writers.
The few things I've check this way were correct, even revolvers with safeties and silencers.
Yup, they do exist.
 
Many parts you wouldn't otherwise suspect can leave a mark. I have a magazine that leaves very distinctive scratches on the case. And then, there is still the breech face, the firing pin, the extractor, and the extractor.

Also, polygonal rifling is very problematic since it doesn't leave nice grooves on the bullet.

I also found this:
http://www.nij.gov/training/firearms-training/index.htm
 
Along a similar line of thought, if a criminal shoots someone, then goes to the range and fires off 500 rounds -- won't that change the way the barrel now marks the bullets? I mean unlike fingerprints, rifling changes with each shot and won't grow back.

Then think about that pre-fired case that came with the gun. It's supposed to allow for crime scene collected cases to be matched to a particular gun. But, I've never heard of even one single criminal that was convicted because of that information.

All this theoretical thinking makes my head spin! It's still best to not get yourself into crazy situations like that !
 
The safest bet for said criminal would be to torch that gun into very small bits, go on a road trip, and chuck them far and wide. Said criminal would be silly in his head to keep the gun and attempt to fool the lab. Thankfully most of them are impulsive, drug addled, and stupid. Most but not all.
 
FWIW, I recall a case from Stuttgart, Germany back in the day, where a GI was murdered by another soldier. The killer got rid of the pistol, but we found a magazine and some cartridges in his possessions. The lab was able to say, within a reasonable degree of scientific certainty, that the shell casings found at the crime scene at the 5th General Hospital had been stripped from the magazine found with the suspect. :cool:
 
I would say they will match the bullet to the very barrel. No two barrels will ever produce the Exact markings, even two barrels made one after the other.
Click to expand...

One could argue that a barrel will never fire two bullets with the exact same markings either. After every fired round the barrel is left in a condition different from the one before.

Even if someone were to swap a barrel. When a gun is tested for evidence and the pin, extractor, ejector, magazine marks match up and the barrel is the only thing off, they will be looking for another barrel or evidence that you owned one. If a slide doesn't show proper signs of wear to a currently installed barrel could also be another give away, there could be wear marks on a slide where one of the barrels doesn't make sufficient contact at.
 
With regard to the point that two guns from a factory can't possibly be very different...

Have you ever heard the term "lemon" when referring to a firearm? Probably. If a factory can produce one gun that works, and another that doesn't, then it seems well within reason that the same factory could produce two barrels that are just ever-so-slightly different. Remember that these differences are compared under a microscope.

The point to ballistic testing is to say that X bullet came from Y gun, with a reasonable amount of certainty. If the only result you could draw from it was X bullet came from a 9mm Ruger, you wouldn't have much of a case.
 
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