Monday, July 16, 2012

Ballistics - matching bullets

Last week I showed you the brilliant photos that Greg Karim and his colleagues use to figure out whether a cartridge casing was fired from a particular gun. As promised, today I'm posting a series of photos that show how the same kind of examination is made on the bullets themselves.

Remember, here's the situation:

A bullet is removed from the body of a victim. It's placed into evidence and locked away. A gun is found on a suspect, who's now a hundred miles from the crime scene. The gun is also placed into evidence and locked away.

The essential question this time is: was the bullet from the victim fired from this gun? If so, that's some good evidence. If not, we need to know that too, so we can find the right murder weapon.

So, APD firearms guru Greg Karin retrieves the bullet and the gun from the evidence locker and retreats to his lab.As before , he fires the weapon into a barrel of water. He'll do a number of test fires, fifteen for example. Then he will put the bullet from the victim under a microscope, examine it, and take close-up photos. He will do the same with the test-fired bullets.

This is what he'll see:

Now, you'll see reference on these photos to two types of characteristics: class and individual. The examiner is looking to make matches in both classes, and here's their basic definitions:

Class characteristics can be defined as:
Intentional or design characteristics that would be common to a particular group or family of items.
The class characteristics of firearms that relate to the bullets fired from them includes the caliber of the firearm and the rifling pattern contained in the barrel of the firearm.

Where individual characteristics are:
marks produced by the random imperfections or irregularities of tool surfaces. These random imperfections or irregularities are produced incidental to manufacture and/or caused by use, corrosion, or damage. They are unique to that tool and distinguish it from all other tools.


  1. But let's just say, for example, you've got a round that was fired from a Ruger LCP .380 and you're comparing it against a Ruger LCP .380 that you obtained from a suspect. How do you know it came from THAT Ruger LCP? Wouldn't all Ruger LCP's fire the same way? Just wondering.

  2. Good question. But no. :) My understanding is that the individual characteristics that an examiner sees come from the differences in the way a gun is treated over the months/years. A gun that's never cleaned, is knocked about, is used a lot, etc will show different individual characteristics than one that's not. Now, I'm guessing that two brand new guns of the exact same make and model might pose some problems.

    There are also something called striations, which are very small impressions onto the sides of a bullet made by minute chips of steel that embedded themselves in the barrel of a gun during the manufacturing process.

    Lisa, you did shoot someone with a Ruger LCP .380, did you? Just wondering...;)

  3. This was so interesting! I have never fired a gun and kind of want to, just so know how it feels (for a future book, I swear).

    I'm going to have pick your brain about this stuff sometime (over a drink, which I'll buy, I promise).

  4. Sure thing, Jenny, I look forward to it. Been some time since a woman's bought me a drink, come to think of it. :)

  5. But wouldn't this method fail to account for any damage to the bullet that occurred upon entry, especially if a bullet passed through someone and embedded itself in a wall? Further, what is the scientific standard for accuracy? How close is close enough?

  6. I think it does take account because if they kinds of damage you mention happens and distorts the bullet too much then no match will be made. And I think each jurisdiction has its own guidelines as to how many similarities or identifying marks must exist before a match can be pronounced. That's one of the things I admire so much about our own Greg Karim, he's very strict and takes his professional reputation very seriously, he won't shade it for anyone, which means when he tells me there's a match I have great confidence.

