Updated: Dec 9, 2022
Carbon ring is one of the more controversial topics when it comes to shooting. What really is it? Is it bad? How does it form? Does the carbon ring cause velocities to become erratic? Let's dive in and talk about what is going on and how to mitigate it.
Let’s say in a scenario you have seriously neglected to clean your barrel after many rounds. You go to the range, start shooting, and notice that your speeds are all over the place and your rifles are not shooting accurately. You begin to wonder "what the heck is going on?" You know the barrel is somewhat newer, it’s not near the end of its life span-should we just put a patch through it and clean it? We go ahead, clean it, shoot it again, and still something is wrong.
You finally start inspecting the inside of the barrel; specifically the leade and throat area (figure. 1), and find some serious carbon ring. (figure. 2).
What is carbon ring and where is it in the barrel?
The carbon ring or pressure ring is specifically formed by high pressure, carbon, plastic, and metallics that form right in front of the case mouth (figure. 3) and the start of the leade during firing (figure.4 ). This results in issues like cases not eventually chambering or even increasing pressure which translates to velocity becoming erratic.
Does Trimming brass short do anything? How do we mitigate carbon ring?
Luckily, there are some ways we can mitigate pressure ring. Some of the reasons it forms are because of poor cleaning methods, metallics left over in the case, soft jackets, worn throats, or the biggest culprit...which is trimming!
Trimming your brass too short is bad. To elaborate further, if you have a case neck that is trimmed short a few things can happen.
Since a lot of pressure is concentrated at the case neck during the firing sequence, any materials like brass shavings or other materials under high pressure are essentially flash forged in the highlighted circle (figure. 5). If you have really bad concentricity issues and the projectile ends up scraping within the red circle area (figure. 5) which is an open void of where the neck should be covering, that also deposits and the material and is forged under high pressure to create pressure ring. In other words, shorter cases are going to cause more metal deposition by way of scraping and heat which will deposit in the area of where the neck should be.
What length should I trim my brass to?
To figure out how short is too short, we should talk about chamber lengths.
Even though your manual has advised of a trim length and depending upon the situation where you might just trim all your brass to the shortest length in your pile of brass, it can increase the pressure ring. So, to figure out where we should be trimming brass, you should take a look at your chamber's overall length. You can use this little $6 gauge here from Brownells which we show how to use in our video and walk through carbon ring in more detail in the video.
So now that we know what causes pressure ring, and what pressure ring is, it is advised to trim your cases when you are within 0.005” of your max cartridge length. Of course, trimming cases to the same length for consistency before reaching that point is always recommended as well. Moreover, the point is to be weary of trimming brass too short.
I personally like to let brass grow a couple of firings before trimming (during the fireforming process) before I trim them all to the same length and let them continue to grow. Hopefully, this will help you a little bit more in diagnosing what a carbon ring looks like and what causes it.
Thank you for reading! If you are interested in learning how to reload or are an experienced handloader looking to learn how internal ballistics works to significantly cut down on load development time you can find our classes here
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