Forensic Ballistics

G

GilaMonster

New member
...or, maybe more properly called ballistic forensics...

Am reading Michael Connelly's latest Harry Bosch/Mickey Haller novel, The Brass Verdict.

In an early chapter, the lawyer finds that the police know what gun his client's wife and lover were killed with: "Though the murder weapon was missing, a [police] report said that slugs had been identified through ballistic markings as coming from a Smith & Wesson model 12, a .44 magnum revolver."

Later on, another homicide shooting: "I knew that by studying the markings — lands and grooves — on the slugs they would be able to tell what kind of gun fired the rounds ... the investigators knew what gun (a Beretta Bobcat .25) had been used, even though they didn't have it."

Obviously, I know that crime labs are able to identify rounds that came from a particular gun -- by comparing them to other bullets fired from that gun. But, can recovered slugs really identify (blindly) the gun manufacture and model from which they were fired?

Does anyone here know if that really is possible? Or is this just what I suspect it is -- 'Hollywood fiction'?

DOUGinPINE
 
No.

To explain further, depending upon the condition of the bullet, experts may be able to tell little about the gun from which it was fired. Even when recovered in good shape, ballistic experts normally cannot even identify the exact caliber of weapon. For example, they may only be able to say a bullet came from the .38 family which would include .380, .38 spl, .357 magnum and others. Depending upon condition of the bullet, they may be able to identify the twist rate and direction of a gun's barrel. This may act to exclude a certain handgun or model of handgun, but there are enough guns with similar rates and direction of twist, that they could not say a bullet came from a particular model of gun.
 
Last edited:
Having worked in CS investigations and as a certified CSI instructor, I'll tell you what you see on TV or read in books is as differant as night and day.
 
It depends on a lot of things. If you get a bullet in good condition you can make a number of measurements from it.

1. You can generally determine caliber from the weight, diameter & style.
2. You can determine the type of rifling (ballard, microgroove, polygonal).
3. You can measure the twist of the rifling.
4. You can measure the number of lands & grooves.
5. You can measure the width of the lands & grooves.

From there with some information from various manufacturers you can probably make a good guess at what manufacturer made the gun and might be able to narrow the gun down to a range of models.

It might, for example, be possible to tell that the bullet was from a S&W .44 magnum revolver but it would, of course be impossible to tell if it was a Model 29 (blued steel finish) or a 629 (stainless steel finish).

If you had a 180gr bullet with a diameter of .40", a rifling twist of 1 turn in about 9.8 inches and the rifling was polygonal you could be pretty sure that it was fired from a Glock or H&K pistol. You could rule out the 10mm because the twist rate is wrong so now you know that it's a .40S&W pistol. The H&K and Glock implementations of polygonal rifling are slightly different so you could probably narrow it down to one manufacturer or the other. Determining the specific model would be impossible.
 
ooops - I mistyped --- he said it was a Smith model 29, not "12"

good catch!
Click to expand...

I figured it was Connelly, not you, that made the mistake. It's the kind of error you see quite often in fiction novels.
 
If you had a 180gr bullet with a diameter of .40", a rifling twist of 1 turn in about 9.8 inches and the rifling was polygonal you could be pretty sure that it was fired from a Glock or H&K pistol. You could rule out the 10mm because the twist rate is wrong so now you know that it's a .40S&W pistol. The H&K and Glock implementations of polygonal rifling are slightly different so you could probably narrow it down to one manufacturer or the other. Determining the specific model would be impossible.
Click to expand...

Of course the writers of the popular CSI TV shows would have you believe that microscopic trace from the barrel would be on the bullet. A mass spec analysis would reveal the chemical makeup of the barrel metal. Then all it takes is a quick trip to their magic computer database and you instantly have not only who made the gun and when, but the original purchaser along with his/her picture.

CSI has probably done more to derail the criminal justice system in America than any defense lawer could ever dream possible. Potential jurors really believe evidence like this can and should be mounted against any defendant.
 
Of course the writers of the popular CSI TV shows would have you believe that microscopic trace from the barrel would be on the bullet. A mass spec analysis would reveal the chemical makeup of the barrel metal. Then all it takes is a quick trip to their magic computer database and you instantly have not only who made the gun and when, but the original purchaser along with his/her picture.

CSI has probably done more to derail the criminal justice system in America than any defense lawer could ever dream possible. Potential jurors really believe evidence like this can and should be mounted against any defendant.
Click to expand...

I'm sure it's convicted more than it has freed, however... just as "COPS" has convinced millions that violating one's Constitutional guarantees is "normal, good policework". Both are horrible.
 
JohnKSa said:
1. You can generally determine caliber from the weight, diameter & style.
2. You can determine the type of rifling (ballard, microgroove, polygonal).
3. You can measure the twist of the rifling.
4. You can measure the number of lands & grooves.
5. You can measure the width of the lands & grooves.
Click to expand...

I have sincere doubts that an expert could testify with enough certainty for this to be introduced in court in many cases. I leave open the possibility that one could testify about a particularly odd-ball combination of rifling, etc. My previous comment was based on observations from real life criminal trials. For example, in a murder case in which I had some involvement (the legal end, not the shooting end), the FBI ballistics examiner could only testify the bullet was in the .38 caliber family and named several calibers that included. He could testify to the twist rate and that it was a left hand twist. That's it.

Taking an educated guess to say that a particular style and weight of bullet probably was of a specific caliber is not enough. Did that 158 gr. SWC come from a .38 spl or .357 mag or maybe even a .38 SW? Too, even slight bullet deformation means exact diameter probably can't be measured -- is the diameter .355 or .356 or .357? While we are free to use these "probably" guesses on forums and so forth, I certainly wouldn't want a person's life hanging on an educated guess.

I'll give you an example. The FBI's experts testified for years that they could use the specific alloy make-up of fired bullets to determine brand of ammunition. Then, they discovered they really couldn't and now refuse to do so. I know of at least one murder case where this resulted in a new trial and ultimately led to a plea to a reduced charge and minimal sentence.

I am most definitely NOT an expert on ballistics and have only knowledge gleaned from my exposure to legal proceedings. It is possible I am wrong about some of this and am open to correction.
 
There are certainly situations where you would be limited as to what you could determine even with a bullet in good condition. The .38SW/.38sp/.357Mag situation would be one of those situations that would limit what you could determine. However even though you probably wouldn't be able to nail down the caliber you might still be able to narrow it down to a manufacturer based on the rifling pattern (twist rate, # of lands & grooves and their dimensions).

As to what would hold up in court, that's another topic altogether and one that I'm sure that I'm not qualified to discuss.
 
I agree with JohnKSa- while you might not be able to say with all certainty what gun a bullet came from, the information gleaned from a recovered bullet along with all other evidence, can, and has been used to convict a person.
Real life CSI is a far cry from the BS on TV. I've yet to talk to anyone in LE or the legal practice, that has any use for the TV show. Most say the show has made their job a lot harder because people believe the show, and expect it to go the same way in a real court.
 
Forensic Ballistics 101: Fired bullets have both class and individual characteristics.

Class characteristics would include the number, width, depth, and rate of twist of the land and groove impressions left on the bullet. They can sometimes be used to establish that a bullet was fired from a specific type of firearm, but more often would only indicate the make and caliber of the firearm (e.g., a S&W .44 Spl or .44 Magnum).

Individual characteristics would include striations left by imperfections in the barrel rifling/crowning process, or damage caused by cleaning, etc. They can be used to link a specific bullet to a specific firearm.
 
Clean cut one test absolute ballistics are a joke. But the TV audience in general doesn't seem to be able to reason beyond that, so the networks give them what they want.

However it's the combination of ballistics info that impresses them eventually.

It's a 124 gr bullet (retained mass) with left hand twist to the rifling.
It's probably a Colt, because of the left hand rifling.

Diameter of the recovered bullet is .361". Ok It's something in a nominal "38" (.36") caliber.

Weight (as recovered) is 124 gr. But the HP bullet has opened up completely. It is Not a158 Gr bullet. But it might have been a 125 gr one. It sure as heck isn't a 110 grain one.

The "famous" mass spec. Has discovered the jacket (& core) metal composition is similar to a brand XX model XXX bullet. It's the combination that counts here. This is cross checked with the balance of weight between the jacket & core, & the pattern of cuts in the jacket to ease expansion.

So now the bullet is washed in the correct chemicals to dissolve powder residue from the base.
That gets run thru flame analsys "AA" (or something similar) the combination of ash & unburnt powder is representative of several similar powders. Let's say 2400 for the sake of argument.

Ok so we have a 125 Gr hollowpoint .357 caliber bullet, combined with a colt revolver, powered by 2400 powder. Probably a .357 magnum colt. No we don't know it was a python (yet).
Now we run the rifling as previously discussed, thru the database of "standard projectiles". They all point to the pattern as being from a Colt Python.

Now we apply known burn rates against the ratio of ash to unburnt powder. Indicates a 6" barrel.

Somewhere down the road we find a suspect owns a Colt python with a 6" barrel. He loads 125 Gr HP bullets over 2400.

THEN we find a case that he fired, but didn't reload, clean, or anything else to yet.

OK so now we match an NMI test to both the case neck & the residue from the barrel. If we don't have a fired case we do a ballistics test to see how similar the results are. ( we do have enough probable cause to take the pistol in for ballistics testing)

We can duplicate the test results closely from the recovered bulet.

So now there is a test for residue from the bullet traces left in the barrel. (the green stuff that Hoppes pulls out).

This is run thru an NMA test series. (Neutron Metal analsys).
The results of the NMA from the bullet residue in the barrel are close to a seperate NMA run on the recovered bullet.

The powder residue is close as well.
If we're lucky the primer glass composition is similar if there is enough rammed into the bullet base/ barrel.

So now we have a pretty good indication, backed up with a battery of scientific tests, all of which corroberate each other that the victim was probably shot with a 125 Gr brand XX bullet fired from a Colt Python 6" barreled revolver. The powder used was 85% likely to be 2400. There is a reasonable correlation between unique "fingerprint" markings & the accuseds gun to indicate that it was very likely to be the gun that fired the bullet recovered.

The accused owns a 6" Colt Python in royal blue. He reloads. He usually loads 125 Gr XX bullets over 13.5 Gr of 2400. (This from his pulled reloads & his reloading records.)

The gun has been fired recently & not cleaned yet.

The residue in the gun matches both the bullet & the powder used to commit the crime. The type of rifling, power / ash residue matches the barrel length. The accused has all the components needed to produce all the tests from recovered evidence at the crime scene.

Binocular microscope bullet comparison find 25 points of coincidence between the sample bullet & the test bullet fired during ballistic testing. 18 of them are "batch related" they could be made by any 6" barel Colt Python. The rest are minor scratches, tooling mark chatter & so on in the exact gun recovered from the accused.

The deceased was known to the accused, due to an affair between the accused's wife & the deceedant. The accused has no alibi for the time frame in which the shooting occurred.

Conclusive proof... nope.
Enough to make the jury think twice about the fingerprint of the accused on the door knob, Oh Yeah baby!:eek:
 
Last edited:
However it's the combination of ballistics info that impresses them eventually.
Click to expand...
Wogpotter -- Congratulations on your imaginative "analysis." You've got a future in writing episodes for CSI. :)
 
I am most definitely NOT an expert on ballistics and have only knowledge gleaned from my exposure to legal proceedings. It is possible I am wrong about some of this and am open to correction.
Click to expand...
Thanks for the compliment (i think):o

This is kind of based on a real case years back when I did this kind if thing for a living.
He had found a way to "fool ballistics", he swapped parts round in a colt type .45 auto, figuring that there would be no match & that the search would just eliminate him right there.

He forgot things like "dabs" on the case & that ballistics fingerprinting can be used on ALL of the bullet & case. He shoulda swapped the slide & firing pin, as well as the extractor & ejector. Had he changed powders & bullet types, or just bought ammo off the shelf, the evidence would have been much slimmer.

The "bright spark perp" was convivted & sentenced.
It's not JUST the forensic evidence, was my point.
 
Yea, then that must be the reason that alot of guns and knives end up at the bottom of the river. Easier than trying to fool someone with fiddling with the gun.
 
You must log in or register to reply here.
Back
Top