Fired Bullet Linked to Make/Model of Gun?

[Bobo]

I see this in movies and TV a lot. The cops recover a fired bullet and some how can magically tell what brand and model of gun it was fired from.

I don't think anyone could tell what BRAND of gun a bullet was fired from never mind the MODEL!

Is there something I'm missing here?

 

[ZeSpectre]

Ahhhh, that TV magic.

There are any number of television "conventions" that are used to trip up anyone planning a crime based on what they saw on CSI.

Some are to make law enforcement seem superpowered, some are intentional alterations or omissions, some are just creative writing to handle the constraints of television.

A one hour TV show (40 min after commercials) doesn't have time to "trace" the gun so they skip right to the identification (makes the heros look super knowledgable and moves the show along).

A few other conventions.
-"Keep 'em on the line so we can trace it". Hah, the instant the phone system makes a connection the switching computers know how it's routed.

-Suicide by wrist slitting always shows people doing it -across- the wrist. This is the least fatal way of doing it and the easiest to bandage back up to save the person so this is the way it's shown.

-One shot stop (or one stab stop). Again, TV shows don't have time to wait for the badguys to drop so they just fall down once shot and the plot moves on.

 

[Geno]

Here's one...don't foget the 6-second strangulation!

 

[N3HCP]

Some guns do have distinctive characteristics. For instance, most Glocks use polygonal rifling so a bullet fired from a Glock is distinctive. The marks left on the primer can also sometimes suggest the brand. I can usually tell what brass has been fired from my Glock 23 or 27. The mark is not like any other .40 brass I have seen at the range. As far as the model, I doubt you could tell one model from another within the brand. The marks left by my G23 and G27 are identical to my eye, at least.

I understand that the number of lands and grooves and the twist (right or left) can be used to identify some other brands.

 

[Hoppy590]

the one punch knock out is always a good one.

 

[El Tejon]

Works better by elimination.

 

[Tommygunn]

To match a specific bullet to a specific gun, they have to have a mystery bullet, and a bullet known to come from suspect gun. The rifling in the barrel leaves striations on the bullet unique to that gun, and they can match them using a comparison microscope.
If all you have is mystery bullet X, you can tell caliber, and from the direction of the rifling you might be able to eliminate all makes of guns that have the opposite twist to the rifling, but that's it. If you have a case you may be able to know the brand name because some particular handguns have unique firing pin marks, but not all. Extractors also leave marks that can be matched to a particular gun -- but again, you need the gun.

-"Keep 'em on the line so we can trace it". Hah, the instant the phone system makes a connection the switching computers know how it's routed.

In 1967, this was true; you needed to keep them on the line for a few minutes. Now, computers do it near automatically. Once the connection is there, you can track it even if the boogieman hangs up a second afterwards.

 

[Dave P]

the one punch knock out is always a good one.

... of the 220 lbs bad guy, vs the 110 female!


Tracing bullets: you must be watching the NY lawyer show. Where they ALWAYS find the owner of the registered gun in 5 min or less!

 

[Big Calhoun]

My understanding is that it is possible, once the actual weapon is recovered and test fired. But by in large, without mandatory gun registration across the board and what would be a very expensive and comprehensive database, it's mostly 'TV Magic'.

Oh...you guys forgot one...the one stop shot with no loss of blood.

 

[Geronimo45]

"Keep 'em on the line so we can trace it" - coppers still don't have Caller ID, I guess.

 

[quatin]

the one punch knock out is always a good one.

this one is actually real. people have gone down real quick on ifl from a good punch.

 

[Carl N. Brown]

Cartridge casing marks

Relationship of ejector marks to extractor marks can
help identify (or eliminate) make or model of gun in ID.
(obvious one: all semi-auto pistols that use the
firing pin as the ejector (Raven MP25))

Bullet marks

Number of grooves in rifling.
Depth of grooves.
Width of groove versus width of land.
Direction of rifling twist.
Rate of twist.

These can help identify (or eliminate) make or model.

It is not foolproof nor as easy as it is in the movies/TV.

And that is just ID'ing make or model from case or bullet.

Individual markings--the microscopic marks that might tie
an individual case or bullet to an individual gun--are all
subject to wear, tear, erosion, corrosion; in fact, some are
caused by wear, tear, erosion, corrosion, abrasive on bullet,
slip of cleaning rod, random accident. Matching a factory
fired casing to a casing fired from a gun that has not been
preserved New-In-The-Box NIB is also not easy.

The only matching that reasonably works is tying cartridge
case or bullet recovered at crime scene to test bullets from
of a gun recovered from a suspect. That is not a slam-dunk
either. If the barrel is worn or pitted, the microscopic scratches
could be left by the leading build up in the barrel.

I have read of a shotgun wad being tied to a specific shotgun
due a defect of the muzzle (bad hacksaw job or accidental
muzzle damage). Otherwise, shotgun wads are pretty
anonymous.

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[Odd Job]

Bobo

There is a big difference between class characteristics and individual characteristics. The former enables the exclusion of various types of firearms, and the latter enables an absolute match to be made to one firearm only.
A very good site to read up on all of this is FirearmsID. Here is the link:

http://www.firearmsid.com/A_FirearmsID.htm

 

[TexasRifleman]

"Keep 'em on the line so we can trace it" - coppers still don't have Caller ID, I guess.

In real life the phone companies used something called Lawful Intercept under a law called CALEA; Communications Assistance for Law Enforcement Act.

It's very easy. With a proper username and password LEOs can log into a phone companies database and see the call, and in some cases listen to the call live.

My company makes a lot of the equipment.

It's frighteningly simple, and why I don't talk about ANYTHING on the phone

There is no time requirement, the info is there as soon as the call is connected.

 

[Firehand]

Rifling marks or primer/case marks can help define a make of firearm, but actually matching it to a particular one is not nearly as cut & dried as movies/tv makes it seem.

Check out smallestminority.blogspot.com, on the left sidebar there's a link to 'why ballistic fingerprinting can't/won't work' and check it out. Very good rundown on this.