Blog Archives

Ever Wondered if an AK-47 Will Fire Underwater?

I’m a sucker for these types of videos and I figured a few of you might be too.  Some people question whether a gun will fire under water and what the effects might be.  As you’ll see in the below video, the gases released during discharge react differently in water than they do in air but the video does give you some idea of where and how the gases and GSR are expelled from the firearm. Obviously you could never recover GSR from a suspect firing a gun under water but the video is neat nonetheless. I thought it was especially interesting to see the cycling of the weapon was faster under water than in air too. Enjoy.

Laser Mapping a Crime Scene

Leica_ScanStation_P20_PIC_180x180I have been a bit AWOL lately.  Every now and then I need a vacation and this last one turned out to be quite a little adventure. So today I thought it would be interesting to talk about the next generation of crime scene mapping. When I first started crime scene work we used metal tape measures and did our crime scene sketching on large pads of paper. While paper isn’t obsolete, the next generation of crime scene mapping offers many advantages. Tape measures are a pain in the butt. They bend, they come loose, and sooner or later you drag one through a pool of blood (yuck!).

Over the years CSIs have been utilizing various laser based measurement devices. They vary from small hand held range finders (great for inside measurements) to Total stations (like the ones you see surveyors using). Near the top of that list is the automated laser based scanner. These types of units gained international exposure during the reconstruction of the car accident claiming the life of Princess Diana. These units are not in common use yet due to the cost (some in excess of $100,000.00) but more and more agencies are beginning to use them.

The above video demonstrates one such unit from Leica instruments. I’ve used a number of Leica products and found them to be top notch. The scanner is about the size of a small trash can and mounted atop a surveyors tripod. Once activated the unit will bombard the crime scene area (up to a distance of nearly 1000 feet)  with millions of laser pulses which bounce off various surfaces and return to the unit. It will scan a full 360 degrees and 270 degrees above and below the unit. Basically everywhere except the unit location. A typical room can be scanned in a few minutes. CSIs can also link the unit with GPS which is really handy in outdoor crime scenes (especially ones in remote locations). The units can even operate in complete darkness.

Those millions of points create an exact three dimensional map of the scene that can be represented in a rotational diagram. It even records color. Utilizing the scanner software this virtual map allows CSIs to determine distances between any objects in the scene. No more missed measurements and the accuracy is phenomenal. The CSI can also zoom and pan around the image to view evidence from different perspectives. As you can see in the video, certain points can be hyper-linked to crime scene photographs or even text reports. This is a powerful tool for the reconstructionist and can be useful for prosecutors as well.

This is cutting edge stuff and you may want to consider using this technology in your next novel. Remember, this unit will record everything visible to the laser so it may even “find” a piece of evidence missed by your detective. Maybe your scene was mapped at night (dumped body or car accident) and a crucial piece of evidence wasn’t seen by the on scene responders. Then your protagonist can go back and find the crucial clue. Use your imagination and have fun with it!

The Value of Firearm Ejection Patterns

White tent placards showing shell casing locations

A lot of researchers have studied what examiners refer to as “ejection patterns”. This is the arrangement and dispersion of fired cartridge casings found at a crime scene. The theory is pretty straight forward; cartridge casings will be ejected from a firearm in a predictable manner that will provide insight into the shooter’s position when firing. Unfortunately, the chaism between theory and reality can get pretty wide.  Semi-automatic, or self-loading, firearms are designed to extract and eject fired cartridge cases to make room for the next live cartridge in the magazine.  Most modern firearms are designed for right-handed shooters and will eject the cases to the rear and right of the shooter. Having said that there are some weapons designed for left hand shooters which eject to the left and still others that eject downward out the bottom of the weapon. The key function is to keep the spent casing from hitting the shooter.

The problem with the use of ejection patterns is that there are a lot of things that can and will influence the manner in which the casing comes to a final rest. First, the manner in which the weapon is held during the firing process. If the gun is held “sideways”, sometimes referred to as “gangster style” with the ejection port facing up, the casing will eject differently than if the weapon was held normally with the sights pointing up.  The elevation of the weapon is another consideration. Is the person shooting from the hip or shooting with the weapon at eye level (or both)? Then you have to consider the movement and orientation of the shooter.  Is the shooter firing straight ahead of them or to their right or left? Are they moving (running and shooting) or are they stationary? You may never know these things with certainty, especially if the weapon isn’t recovered. All of this is bad enough but we haven’t even begun consider the many factors.

Aside from the weapon design and how the shooter fires and moves there is the environment. Is the shooting indoors? If so, the casings may be hitting other objects like walls, furniture, chandeliers, etc. that can alter the “flight path” of the casing.  If the shooter is outdoors are there over-hanging branches from a tree? Is there a strong wind? We also have to consider the surface the casing lands on.  Surfaces like snow or a lush green lawn may help to “catch” the casing and allow for very little movement. Other surfaces like cement, linoleum, or tile may allow the casing to “bounce” and change direction. Then there is the slope of the surface. Envision a casing that hits a roadway versus one that hits on the sloped area of the sidewalk leading to the gutter. Think of a cartridge casing like a little football. We all know how unpredictable a bouncing path for a football can be right? Well, casings can act in a similar manner.

When all of that is said and done we still have to consider any “post-shooting” processes that may change the resting position of the expended casing.  Cartridge cases are small and can easily be moved if they are kicked, stepped on, driven over, or by other actions.  There are a lot of first responders like police, paramedics, medical examiners, even by-standers or family members that may also inadvertently move these casings before the CSI shows up on scene.

The above video shows both slow motion and normal speed ejections. Notice how varied the flight paths are for the same weapon with a static (stationary) shooter. Also, about half-way through the clip you will see one casing actually hit the camera and bounce back towards the shooter.

You might read references to police using ejection patterns in novels or see them on a television show but the analysis is not nearly as straightforward as they might seem. In fact, some studies have shown as much as 25% of casings don’t even eject in the manner or direction as designed. That’s not too surprising actually. Gun manufacturer’s don’t really care about exactly where the casings eject or how consistently they eject in the same manner as long as they stay out of the shooter’s face.  Now ejection patterns can provide some general insight into the general location of the shooter but you just have to be very careful about how far you take the reconstruction. So the key is to recognize the many influences that can vary the resting position of the cases.  If you want to have some fun with it you could have an expert rely too much on the locations of the casings only to find out later that they had been moved through some other action. That could really throw your analysis into a tailspin.

Is That Cordite I Smell?

Not unless your novel is based in a pre-WWI era. This is one of those terminology mistakes that seems to have kept a foot hold in modern crime and suspense thrillers. I’m listening to an audio book during my commute and the NYT best-selling author has referenced the smell of Cordite several times in the modern tale. Perhaps it’s a little thing that a lot of readers may not notice but it is a glaring error to knowledgeable readers. The fact that such a well regarded author (one with a reputation for doing good research) makes this mistake tells me that many other authors may make the same error. Truthfully, it’s a simple error to make but even easier to avoid.

Cordite was a type of smokeless propellant for firearm cartridges developed by the British from the early 1890’s to about the end of WWI when better smokeless powders were developed. It was still used in heavy guns (like tanks) to varying degrees but it is not produced anymore and certainly not for modern firearms. It produces an acrid smell like burnt acetone if you can imagine that. Modern smokeless powders produce a much less noticeable odor. The smell of modern powders don’t “hang in the air” unless you’ve discharged dozens or hundreds of rounds in a confined space. That’s not to say a seasoned CSI or detective couldn’t detect an odor after a few shots were fired but it just wouldn’t be as pungent or last very long (minutes) in most cases.

So if you’re writing a modern novel avoid descriptions like “After emptying his magazine at the knife wielding thug, Butch Big-guns nearly gagged on the curtain of cordite hanging in the air”. You are of course welcome to use the character name Butch Big-guns if so inclined :)

Understanding Rifling in Firearms

The lands and grooves inside a cannon barrel

Rifling is a term that refers to the grooves machined into the barrel of a firearm to impart a spin on the bullet during flight. This spin helps stabilize the bullet thereby improving accuracy and increasing the distance traveled. The raised ridges traveling along the length of the barrel are called lands and the grooves are the spaces between. These lands and grooves also have a “twist” or slight rotation to the left or right (depending on make and model) which creates the spin. The number, width, direction of twist, and rate of twist can vary between makes and models. The degree of this twist is called the “twist rate” and is expressed by how many inches it takes the projectile to make one full revolution of the rifling. For example, a barrel with a 1:12 rate of twist means the bullet will make one full revolution every 12 inches of the rifling.

Rifling is found in most modern rifles and handguns (even muzzle loaders) with the exception of most shotguns which are referred to as “smoothbore”. There are different methods for machining gun barrels but generally speaking, the tools that manufacturers use to create these lands and grooves leave unique marks (scratches) on the lands and grooves. As the bullet passes down the barrel the lands and grooves will replicate these marks onto the projectile. Firearms examiners evaluate the rifling in two main ways.

First, by looking at the gross physical features (called General Rifling Characteristics; GRC) of the lands and grooves (number, width, and direction of twist) the examiner may be able to eliminate certain makes and models of firearms. The FBI maintains a database of GRC from firearms all over the world which is updated once a year and distributed to the firearms examiner community. From this an examiner can create a list of possible gun models that share the same GRC as the crime scene bullet.  When a known bullet is submitted to the lab the examiner can compare the presence and location of these rifling marks on the crime scene bullet to the known standard to determine if that gun was the one that fired the bullet. I’ll have more on this process later as it is much more detailed than what I have allowed for here.

Rifling marks on fired bullet

Suffice it to say that firearms examiners use these marks to include or exclude a gun as having fired a particular bullet. If you want to put something interesting into your story choose a gun that has unusual rifling marks or general rifling characteristics. This may be from a rare or antique firearm, an after-market barrel, or a custom-made one. Your local gunsmith may be able to point you in a good direction. Then your characters can spend a few scenes trying to unravel the mystery of what kind of gun was used in the shooting. Another thing you might consider is using a gun in which these rifling marks have been damaged or destroyed intentionally by the criminal (like using a drill bit to mar the barrel). Use your imagination and have some fun with it.

Please Load Your Gun with Cartridges

Many of my articles deal with using the proper terminology and this one is no exception. I don’t like to sound too critical but I believe it is important to be accurate in the small details of our novels. One of the most frequent mistakes I read in novels or see on television is the use of the term “bullet” instead of “cartridge”. Even experts can interchange the meanings of these words. Recently, a firearms examiner I know called to ask if I had any .45 caliber bullets for an experiment he was conducting. Being a re-loader I did but as the conversation progressed I had to clarify “do you mean .45 cartridges?” to which he laughed and affirmed. It was a simple, innocent, exchange of terminology but if you don’t like e-mails pointing out the mistakes in your novels here is the difference.

The bullet is the conical shaped projectile of the cartridge. The bullet is the piece that leaves the muzzle of the gun and travels towards the intended target. The cartridge case is the brass or steel part that holds the primer (the ignition source), the gunpowder, and the bullet. When all of the unfired components are assembled you have a cartridge. If you load a cartridge casing without a bullet or insert a bullet without a casing holding powder and primer you won’t project a bullet.

One big exception is a muzzle loading rifle sometimes referred to as a “musket”. These weapons are characteristic of the type used in the American Revolutionary War but are still manufactured and used today by collectors, hunters, and competitive shooters. I will have future articles on muzzle loading weapons but those are not used by police or most bad guys. So if your character is loading “bullets” into a gun or magazine you’re technically incorrect.


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