Bullets and Gun Barrels: An Easy Comparison?
Rifling is the term used to describe the twisting pattern of grooves and lands (raised areas between grooves). Lands and grooves are tooled into steel gun barrels to cause the projectiles (bullets) to spin. The spinning movement stabilizes the bullet, causing it to travel straight and true, sort of like how a football spins when thrown by a quarterback.
Gun barrels start out as solid pieces of steel.The center hole is cut using a drill. Then, the rifling pattern is tooled to the inside of the barrel.
A tool, such as the one pictured above, is forced inside a newly drilled gun barrel, cutting lands and grooves as it passes through.
When a barrel is manufactured, marks caused by contact with machinery are left in the steel. These blemishes are different on each barrel, causing individual guns to have distinguishable fingerprints. No two set of markings are the same. Also, normal use of a firearm can cause distinctive markings inside the barrel.
Bullets are made from soft metal, such as lead. As they pass through a rifled barrel, the imprint of lands, grooves, and tooling blemishes are permanently stamped into the projectile.
Investigators use each of these markings to match bullets with the gun that fired them.
Spiral pattern of lands and grooves
Bullet with impressed image of lands and grooves in its surface
Gun stuff for fun…
Caught by surprise
Don’t monkey with me.
No way I’m hunting with Dick Cheney.
I told you I’m sick of canned food. I want real fish, and I want it NOW!
For those of you who couldn’t make it, Forensic University hosted a day at the gun range for members of Sisters in Crime.
The new Bond.
* BREAKING NEWS *
POLICE PROCEDURE AND INVESTIGATION has been nominated for a prestigious Macavity Award! I’m truly thrilled and humbled to be included with such a star-studded group of authors. What an incredible honor. Thanks so much!
Sorry about the owies, Lee. Hope things get fixed up soon.
Hi Jennifer – I’m one of those white knuckle flyers unless I’m at the controls. Most of my time is with reciprocating engines, have only a few hours jet time. But, I do know what you mean about the jet engines, and that engines in general prefer to work than to not. Thank you for the reassurance 🙂
Lee, hope they quickly find the problem and even more quickly come up with the solution – very ouch!
Oh, Lee, ouch! Feel better soon.
Elena – You may not want to hear this (stop reading now if you’re a skittish flyer), but I used to be a designer for jet engines. The manufacturing process for jet engine parts results in a LOT of variability. Probably more than for gun barrels, since part of the finishing process often includes manual tasks, such as sand-blasting by hand. Inspections are in place to make sure parts meet tolerance, and testing happens at the end to make sure the engines as a whole meet FAA requirements, but mainly the design must be incredibly robus to account for inevitable differences in the final product. (This should make you feel better, really! Engines are incredibly tolerant of problems.) Pretty much nothing can be manufactured to have one part to the next be identical. Great for matching bullets and guns!
Ouch. We are supposed to be wishing you good luck, not get well. Hope you are ok. Keep us posted.
Ouch, Lee. I feel for you. I’ve been poked in the spine a time or two. I hope everything checks out okay. Although sometimes it’s more frustrating when all the tests turn up negative.
Sorry I haven’t been around today to address your questions. I was in the hospital for more tests to try and learn why I’m experiencing such excruciating pain in my back, neck, and arm pain. Today, I went through a spinal tap. Let me just say this…OUCH!
Upon contemplation I think perhaps my confusion is a factor of scale. Manufacturing is an attempt to make multiple identical units – one wouldn’t want even an infinitesimal difference in critical areas such as aircraft engines. However, it occurs to me that perhaps cylinders, since they are bored also, have similar markings which are fortunately too small to bother the workings of the pistons.
Oh where is a machine shop when one needs one!
SZ – both my guys were four week babies when they arrived – one is now 17 and very sweet, the other is 15, twenty-five pounds, and was last seen bossing around a rottweiler!
Still remember the every two hour feedings so long ago.
Congratulations on your Macavity nomination. I know I own a copy of your book and it is an invaluable resource. I’m so glad you are being recognized for your work–you truly deserve it!
Hey Terry, congratulations to you too ! Heck isn’t just being published cause for celebration ? If it were me, there would be a link at the top of the page by the cityscape to announce the nomination that goes to all the other categories. Too corny Lee ?
Speaking of kittens, yup, they are a fearless lot. I have four rescues till they are all two pounds. I wanted them to see outside, but they ran straight to the edge of the catwalk. This being the third floor, they don’t go out now. And the knives are well hidden too.
At what point did investigators realize the individual “fingerprint” ? Are guns made this way on purpose just for this use ?
Hey, Lee — you do know I was teasing, right? I think the nomination is fantastic.
And my book is in a list of finalists that includes NYT best selling author Brenda Novak, so I’m proud just to be nominated, ‘cuz no way will I beat out the competition with my little unknown book.
Congratulations, Lee! That’s excellent! When are the winners announced?
Elena – The lands and grooves are the same in every barrel that’s cut using identical dies. But, tiny blemishes occur as metal rubs metal (friction). These cause most of the differences.
Here’s a line from above:
When a barrel is manufactured, marks caused by contact with machinery are left in the steel. These blemishes are different on each barrel, causing individual guns to have distinguishable fingerprints. No two set of markings are the same.
Terry – I just want to make sure everyone knows how proud I am of the nomination. And, please feel free to mention your own work anytime. That’s cool.
i have always wondered why/how the rifling is different in every gun when the same tooling is used to create the barrels. It seems to me they ought to be identical.
Kittens are so cute at that fearless stage.
The Romance Writers of America’s Kiss of Death chapter also held an all-day seminar/workshop/training on firearms at their National Conference in Atlanta two years ago. It included a trip to a gun store (where the staff was a bit overwhelmed at all these romance writers pelting them with questions) and the range, as well as a chance to try out the laser fitted weapons with the training videos.
Hey, are we going to have to congratulate you on the Macavity every day? I could mention one of my books is up for the Daphne, but I’m too cool to do that. You’ll notice I didn’t even mention What’s in a Name?, the title of the book. (Sorry )
I was intrigued by the fact that you use voice recognition software to write. I was watching Wimbledon at the Y this morning and because I need music to keep me pedaling at a decent pace, I use the closed-captioning for the tv. It was a hoot to try to decipher what the commentators were REALLY saying based on the text. And you’ve got that cute accent.