What if there is only a bullet? What general rifling characteristics can do for you.
There are always hypotheticals and wiggle room in forensics, but especially when dealing with general rifling characteristics. Now, this does not mean general rifling characteristics examinations are useless. Like a lot of things in forensics, it is very dependent on the evidence.
As mentioned in my first blog post about the inconclusive result for the bullet that killed Charlie Kirk, the condition of the evidence is always the first hurdle to overcome. Taking a look at the photo, the full metal jacket bullet (FMJ) is in much better condition than the total metal jacket (TMJ) bullet. TMJ bullets have a very thin layer of metal over a lead core that frequently tears and rips away as it travels down the barrel, and especially after it hits an object. The bullet in the photo was fired into a water tank, which kept the bullet overall from deforming, but the jacketing was still ripped away during the firing process. With this bullet, I am limited in the information I can obtain. It is not heavily distorted, so I have some information about the design of the bullet and will be able to narrow down the caliber of firearms that could have fired this bullet. Not much material has been lost, so by the design, weight and diameter of the bullet, it is most likely a 9mm Luger caliber bullet. Although less likely, without seeing well defined rifling impressions from the barrel, I could not completely eliminate a 40 S&W caliber firearm that was loaded with 9mm Luger caliber ammunition (case circumstances could make this more or less likely).
The FMJ bullet is in much better condition. Looking at the cylindrical portion of the yellow colored jacket, you can see rectangles (rifling toolmarks from the barrel) that are tilted to the right (land impressed areas). You can see the edges of those rectangles. The bullet is also not distorted. This is an ideal bullet that much more information can be obtained from.
On this bullet, I can count how many land impressed areas (lands) go around the bullet, and can see what direction they tilt. In this case, six lands that have a right twist (tilting to the right). I can measure the base of the bullet to determine by the measurement, design and weight that it is most likely 9mm Luger caliber. With the other information, I know this is most likely a 9mm Luger caliber bullet with six land impressions with a right twist. This will limit the amount of firearms more than the damaged bullet.
But, 9mm Luger caliber firearms that have six land impressions with a right twist are very, VERY popular.
So, how much weight should we give the evidence? If you are a prosecutor or law enforcement officer, and a suspect has a firearm capable of shooting 9mm Luger caliber ammunition, this would add to your weight of evidence...at least a little. Due to how popular this caliber and rifling design is, it is less valuable. If you are the defense, highlighting how popular this firearm design is lets the jury know how much weight the evidence really has. If your client has never owned or been seen with a firearm capable of shooting 9mm Luger caliber ammunition, this can be a substantial piece of information.
Other calibers of ammunition and rifling designs are much more selective. There have been times I have entered general rifling characteristics into a database and only had a few firearm makes and models returned.
What if there is only a bullet? Without doing the analysis, you may be missing the most important piece of information.
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