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Carbon Ring Build-up, Resulting Problems and a Cure

Though I’ve heard mention of carbon ring build-up it wasn’t until I got to the 6 Creedmoor portion of the large/small rifle primer comparison (last Kauber’s Corner article) was I aware first hand of the problems caused by carbon (powder residue) build up in the bore.

An established carbon ring manifests itself with sudden and progressive spikes in pressure; pressures bordering on the dangerous and in most cases degradation inaccuracy will result. The tremendous amount of heat and pressure transforms carbon fouling into a ceramic coating that is difficult to remove once it has welded itself in your rifling.

Every experienced match shooter, barrel builder, or gunsmith has his or her way of cleaning rifles but most will agree that a hard carbon ring can’t be removed by standard cleaning methods, it has to be scrubbed out. There lies the fine line between effectively removing the carbon ring and damaging your bore by using a compound too aggressive, overdoing the process, or a combination of both.

Not one to attempt to reinvent the wheel or waste time on the Internet trying to decipher the repeated BS from good, sage advice and recommendations, I’ll go directly to those I feel are true authorities based on years of personal experience and an application of said advice in the conduct of their livelihood. When I couldn’t figure out the pressure problems in my Benchmark Barrel built 6 Creedmoor I immediately drove the 20 minutes from home down to Arlington, WA to speak with my long time friends Ron Sinnema and Bill Broderick owner and manager respectively of Benchmark Barrels.

Below is their recommendation for removing the carbon ring:

Cleaning Carbon Ring In Rifle Barrels

Carbon ring in the rifle bore can affect accuracy, pressure and velocity. It is more likely to occur in cartridges with large case capacity and small bore diameter. Carbon ring is best identified with a bore scope and will appear as dark and cracked areas of the bore. It is usually 1”-2” in front of the throat and chamber or within the first 30% of the bore. If you clean every 100-200 rounds in a suspect cartridge you may need to use the steps outlined below. It is ideal to inspect with a borescope to determine whether you have issues with carbon ring build-up and where it appears in the bore.

  1. Clean all fouling and copper from the barrel using your normal cleaning method.
  2. Use a coated rod with a quality jag that is undersize by one caliber – use high-quality flannel or cotton patches.
  3. Fold a patch for a tight fit without sticking, cut/fold appropriately – it is important that your folded patch is tight in the bore almost to the point of becoming stuck.
  4. Most carbon will be 1”-2” in front of the throat and chamber or within the first 30% of the bore.
  5. Put a light coat of Simichrome on the patch being careful to place it on the sides of the patch and the front – this keeps the front of the patch from getting wet and the jag from pushing through the patch.
  6. Push the wet patch all the way through the barrel in one even stroke.
  7. Reapply Simichrome to the same patch as above and clean the first third of the barrel using short back and forth strokes – concentrate your effort on the first 30% of the bore – do this for about 2 minutes being fairly aggressive while keeping in mind that the barrel may warm up slightly, especially with the light contour barrels.
  8. The patch will become loose in the bore during your 2-minute cycle, discard it, and create a new one as outlined in step 3. When you replace the patch during a cycle, do not apply more Simichrome, use the media left in the bore with the new dry patch.
  9. Repeat steps 3 through 8 for ONLY two cycles*.
  10. Clean as normal to remove the residual Simichrome and fouling. The objective is to remove the carbon ring but not to polish the bore to the point of being too shiny.

* If you do not have a borescope, do not exceed the recommended 2 cycle cleaning procedure with Simichrome. If you have a borescope, inspect so you know where to focus your effort and clean until most of the carbon is removed. Some residual streaking etc. is acceptable.

I’ll probably receive a ton of comments about this next statement but I do not recall, after loading and shooting several thousand rounds of 260 and 6.5 Creedmoor with H4350 did I experience much of a carbon ring issue. It wasn’t until I started using RL-16 in the 6.5 to some extent and the 6 Creedmoor primarily did I encounter this problem. When I look down the bore of my 6 after a string, I swear the bore fouling looks the same as the bore of my Shiloh Sharps 1874 45-70 BPCR. Don’t get me wrong though, I’ll continue to use RL-16 in the 6 Creedmoor along with the other temperature-insensitive Alliant powders but rest assured I’m going to stay ahead of the issue by cleaning much more frequently with a solvent designed for carbon fouling removal. So far I’ve had great luck with Bore Tech’s C4 Carbon Remover, though I’m sure there are other solvents that may do just as well.

If you’re experiencing or suspect a carbon ring build-up in your own match rifle, here’s the component recommended for removal of that stubborn ring.

 

Stay Safe,

Jim Kauber
Alpha Munitions CSO

President / Director of Training
The Site Firearms Training Center

9 Comments

  • Ken says:

    Spot on. Been doing this for years except I use Flitz polish. Reloder powders are very dirty in my experience but 16 and 17 give high velocities at low pressure. 17 has a better load density though.

  • Jim says:

    What grit is the Simichrome as opposed to Flitz or Iosso. which of the 3 is the most aggressive and which is the least aggressive??
    Thanks,

    • Thomas Danielson says:

      I do not know about Flitz or Losso but here is the info from the Simichrome website “Simichrome is specially-formulated using the finest micron particle size abrasive of any polish available combined with special cleaning agents. Because the abrasive particles are so fine, Simichrome will not harm uncoated metals surfaces. Unlike chemical polishes, Simichrome will not remove a layer of the metal surface being cleaned. This is especially important on gold and silver plated metal pieces and jewelry.”

  • Robert Weidler says:

    I do a similar process but use VFG felt pellets on their special jag. I keep the felt pellets saturated with C4 and concentrate the work in the problem area. I then follow up with JB Bore Cleaner and Bore Bright. Then finish with a good swabbing with Hoppes 9. Sometimes I will leave the wet felt plugs sit in contact with the hard carbon for an hour or so. Seems to work for me.

  • Max says:

    I seem to be getting pressure spikes in my 280AI but the only evidence of carbon is at the case neck in the chamber. Could this be the cause?

    • Thomas Danielson says:

      This could definitely be the cause. Additionally, carbon will build up in the first 1- 2″ of the throat area and cause pressure spikes. Sometimes they can be quite severe. It’s best to remove any doubts by employing the carbon ring removal procedure as outlined.

      • Max says:

        I am not seeing any carbon on the Lyman borescope in the throat as you described, but I will look again. I am seeing carbon in the area I mentioned in the chamber though.

        Thanks for the great article.

  • Ty says:

    I seldom see a carbon ring problem using RL26 in my 25CM but after a few hundred rounds I use the original reamer lightly turned by hand in the chamber to remove any carbon ring that may be forming but haven’t found much carbon on the reamer. I have used this process on some of you other chambers as well. I understand that many don’t have the original reamer and this would not be possible

  • Matt says:

    Great article, I think the community really appreciates some definitive clarity on the issue. My only thought is, a picture is worth 1000 words, can you post, email or otherwise share YOUR example of the carbon ring? I also am only family with the build up at the end of the mouth. If the carbon 1-2” into the bore is something different than the fire cracking, I’d love to see what you’re referring to. Thanks!!

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