Educate me on this infamous thing called a Carbon Ring.

[mtnbound]

Do you have a bore scope? If not there you no way you can say I have never had a carbon ring. As stated above you may but just don't notice it in the performance of the rifle.

I find that rifles which are over bored tend to develop carbon rings more readily than non-over bored rifles. For example my 7PRC seems to develop carbon rings while my 35 Whelen does not. If you stay on top of them and clean them up before they get to bad they are easy to manage. Only way to know is either with a bore scope or a sudden increase in velocity or loss of accuracy. With respect to velocity you will only know if you routinely use a chronological when shooting.

I did not intend to imply that I have never had one, but I have never experienced the issues others have, like a sudden loss of accuracy that returns after cleaning, blown primers, and difficulty chambering. While I admit I miss targets, I am aware when my systems are not performing as they should and look to determine the cause, which is typically me having a bad day, the wind, or both.
I never noticed anything in my 7PRC.

 

[mtnbound]

It's a real thing, for sure. Why it develops in some rifles but not others, I cannot say.

Sierra had some literature documenting it even back in the 1990's. They didn't call it a carbon ring, they called it 'hard powder fouling' or something of that nature, and described it almost like a ceramic that developed in higher intensity cartridges.

I think with most rifles the gas pressure is high enough that the rifle sort of self-cleans, like an oven at high heat. I can't say why some individual barrels tend to foul in spite of this. I suspect it's a rough barrel finish that gives carbon a place to stick in the first place, but that's only a guess. But I can say that it doesn't seem to be an issue at all with better barrels (meaning those that have higher interior finishes, regardless of other aspects) and lower intensity cartridges, meaning that if you start with a quality barrel and don't hotrod the thing, it's less of a factor.

Thanks. I will dig into Sierra's stuff.

 

[mtnbound]

Correct, here's one in my 6.5 PRC that was actually causing pressure issues after about 40 rounds. Note to self, don't trim brass too short. I cleaned it and measured with a sinclair gauge so I'm only trimming .005" from max case length now. Also need to see if I can get my Hornady trimmer to leave less of a chamfer on the case. View attachment 1021508

Are you loading hot?

 

[Dave Thomas]

Is it due to increased use of suppressors?

No. You'll get it not running a suppressor also.

 

[Castle Rock]

Same, shoot my 6.5 PRC a lot. Didn’t clean the barrel ever, got some pierced primers, learned about carbon rings, cleaned, no issue since. While I don’t love cleaning barrels, I do make an effort to clean them every couple hundred rounds now and pay better attention to if bolt lift starts getting stiff.

Yeah the PRC is really susceptible, and people who are anal about case trimming suffer the most

 

[mtnbound]

Same, shoot my 6.5 PRC a lot. Didn’t clean the barrel ever, got some pierced primers, learned about carbon rings, cleaned, no issue since. While I don’t love cleaning barrels, I do make an effort to clean them every couple hundred rounds now and pay better attention to if bolt lift starts getting stiff.

How many rounds before you start seeing pressure?

 

[Marbles]

Educate me here. Is that dark stripe the carbon ring? I just got a bore scope and I would like to know what I’m looking for.
Thanks

No, in this case the strip is shadow (yellow), red is the chamber behind the mirror.


Here is another shot of an ugly spot without the shadow. It demonstrates why running an oild patch down the bore is a decent idea. Rifle still shoots well, so I haven't worried about it, but probably should.

 

[Formidilosus]

What combo will give me a carbon ring that will cause these problems? What cartridge?

I will have @longrangelead put one together then I will shoot it as is and see if I can get all these issues from carbon rings…. Because so far with hundreds of thousands of rounds from 223’s, 22CM, 243win, 6cm, 6XC, 6UM, 6.5cm, 260Rem, 6.5-284, 6.5PRC, 25/06, 270win, 270 Weatherby, 7-08, 7mm RM, 7PRC, 7mm STW, 7mm RUM, 28 Nosler, 308, 30/06, 300wm, 300 Weatherby, 30-378 Weatherby, 300 rum, 300 Rum improved, 338 rum, 338 Norma, 338 Lapua- and a whole bunch more… all these problems haven’t showed up.


I just can’t seem to find these issues. Shoot2Hunt has a dozen class rifles that a bunch of posters here have shot and shot next to for 1,200 rounds a week- never cleaned, always suppressed- yet somehow none have these issues. The 223 and 308 barrels have no real functional barrel life- 10,000-20,000 rounds. The 6cm’s last about 2,000 or a bit more. The 6.5cm’s last about 3,000 or a bit more. So on and so forth.


But tell me what the cartridge that will produce failure to chamber, blown primers, etc from carbon rings- I’ll get Mike to spin it up and have students shoot it in every S2H class with 12 witnesses. The last one I was absolutely guaranteed would give carbon rings and cause massive pressure issues quickly was 7PRC. That rifle went over 700 rounds without a single thing but bullets going down the bore, the last two 10x round groups it shot were the two best it ever shot, zero pressure issues, zero functional issues at all and I handed it back to Ryan because I was bored.

 

[swavescatter]

You famously don't load over book, and perform minimum prep on brass. That checks off two of the hypothesized causes for carbon ring issues.

So to answer your question, take a Sako S20 6.5PRC, trim Lapua brass to min spec, run 59gr of N565 with Berger 156's and high backpressure suppressor and shoot 400 rounds.