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Gunsmithing Would a carbon ring do this?

Rangemaster

Rangemaster

Step back behind the LINE
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Minuteman
Oct 6, 2013
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High Sierra Desert
We bored scoped my 6cm and it had a pretty bad carbon ring. The brass was not the issue, as it was doing it to at least 10% of the brass in the last part of my match. This started about 50 rounds into the match. I just ordered some bore paste so going to try new brass and a good scrubbing.
812C0B3C-6478-4042-9003-E5A99D2BA980.jpeg
 
BEFORE YOU SCRUB!!!


Get a tight fitting patch, slide it up and stop it right in the throat.
Soak the patch from the backside with carb cleaner and give it a few minutes. Point the muzzle into something that can take carb cleaner or you won't care if it melts.

The Carb cleaner will remove the carbon without abrasive scrubbing that also removes barrel steel...


And a carbon ring can cause spiking pressures but typically a case head separation like that is due to something else.
 
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I have seen lots of discussion about carbon rings lately. I have not read much about carbon rings in the past 10 years on this site. Can someone post a few bore scope pictures of exactly what they are calling a carbon ring? It would be nice to post a drawing of a chamber with the exact location where a carbon ring can form.

I have a Lyman bore scope and have looked in the freebore and throat areas of a couple of my 6.5x47 barrels that have been run with tons of varget and I cannot see anything that resembles what I keep reading about. I would like to see some pictures so that if I ever do see a carbon ring I can readily identify it.
 
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I'm very far from being an expert. I have just 10 years reloading experience. But my instinct on that would be a headspace problem. Case head separation indicates alot of brass stretching. The shoulder denting in is a real weird. This sorta looks like what I would expect a case to look like if you fired a round in a chamber that was much too long, forcing the case to stretch alot before the shoulder hit the chamber.

How many loads on that brass?
 
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I saw the shoulder denting just a couple of days ago. A guy I was shooting with had a couple of case head separations just like this. The rounds chambered perfectly and weren't dented before they were fired. My guess is that the case separation causes a vacuum in the chamber collapsing the shoulder in the form of a dent.
 
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bohem said:
BEFORE YOU SCRUB!!!


Get a tight fitting patch, slide it up and stop it right in the throat.
Soak the patch from the backside with carb cleaner and give it a few minutes. Point the muzzle into something that can take carb cleaner or you won't care if it melts.

The Carb cleaner will remove the carbon without abrasive scrubbing that also removes barrel steel...


And a carbon ring can cause spiking pressures but typically a case head separation like that is due to something else.
Click to expand...

got a bore scope coming before I clean. I was thinking a carb cleaner first before i try a scrub.
 
Skookum said:
I saw the shoulder denting just a couple of days ago. A guy I was shooting with had a couple of case head separations just like this. The rounds chambered perfectly and weren't dented before they were fired. My guess is that the case separation causes a vacuum in the chamber collapsing the shoulder in the form of a dent.
Click to expand...


This was done about 10 times in the last of 50 rounds shot. My guess the pressure was too much and needed a way to escape.
 
Namekagon said:
I'm very far from being an expert. I have just 10 years reloading experience. But my instinct on that would be a headspace problem. Case head separation indicates alot of brass stretching. The shoulder denting in is a real weird. This sorta looks like what I would expect a case to look like if you fired a round in a chamber that was much too long, forcing the case to stretch alot before the shoulder hit the chamber.

How many loads on that brass?
Click to expand...

I know all about this, the brass was five loads with 20 thou on set back. Been doing this a long time, never in countered the dents. I pushed brass to the limits when they split and become thin.
 
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I can get any case to have head separations in 3-5 firings by over sizing in a FL die. Especially semi autos. Indicative of headspace issues.

Carbon ring will cause overpressure and loosen primer pockets, cause ejector swipes, destroy accuracy, etc... Don't think that's your problem. If 0.020" is not a typo, that is definitely your problem.
 
Have you measured a fired case at the area where you are getting the separation? If the chamber is big and the brass is bulging to fit when firing, resizing will work the brass at that area and cause it to crack. A micrometer will show it easily. You can also rub the body of the fired case on a flat hard surface and see if it makes a shiny rub mark on the brass at the same area you are seeing the cracking.
 
Just thinking out loud some more... If .020" set back is really what's happening, it's obvious why the cases are doing that, and obvious why so many are doing that if you cycle them similarly. Load your remaining cases (4-5x fired) the same way, and I'll be next batch you have 50-90% of them do the same thing.

The dents are likely caused when gas escapes through the separation forward of the head, and especially through the mouth, and funnels through the gross headspace void that exists from the .020" setback. The chamber remains sealed to the rear (mostly-- you probably get some gas in your face), but the area in front of the head is in limbo pressure-wise, whether the pressure is inside or outside of the section of brass.

Do you ever have problems with primer ignition? If so, here's your sign... 5x the spec'd headspace allowance.
 
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I also wondered about the dents being due to pressure between the chamber and the brass that leaked out through the separation. But I get mentally stumped when I think about how pressure inside the case should be the same as what leaked out, which should support the brass from collapsing.

Unless... higher pressure escapes out the separation, and gets sealed in by the expanding brass as you mentioned. Then as bullet travels some distance out of the case, pressure inside the case lowers while the pressure sealed between the chamber and brass hasn't changed, and dents case in?
 
.020" bump is WAAAAAAAYYYYY too much. I would verify the shoulder is moving by measuring a fired piece of brass and then again after sizing.
 
On two occasions (during the same match) I had the exact same case head separation (dented shoulder) with Hornady brass with my AI. I had no carbon ring, was not FL sizing, no loose primer pockets and otherwise was following mainstream brass prep and loading regimen. I finished the match with another batch of reloaded ammunition and carefully inspected some of the fired cases and disassembled cases from unfired rounds. What I found was a number of the cases had developed a thinned ring visible only from inside the case when viewed with a borescope. This thinned ring was located in the lower third of the inner case wall. I also noticed that there was a faint exterior ring on the brass which I had earlier mistakenly attributed to either the sizing die or from chambering the round.

While researching causes I found this extract in Accurate Shooter of an article by German Salazar (http://bulletin.accurateshooter.com/tag/german-salazar/) regarding case head separation and fashioned a tool similar to his paperclip method. Using a thin metal rod with a 90 degree bend at the end pushed into the case and pulled back so the tip of the hook rubs against the interior case wall, you can quickly detect the thinned ring. You'll feel a distinct "click" as it rides over the dip. I now check all my brass with this method prior to reloading and cull any brass with a detectable interior thinned ring. Here's a link to the archived full article: https://web.archive.org/web/2013111.../2010/05/reloading-case-head-separations.html

I've passed this tip on to several shooters who have experienced the same case head failure. While I've only seen it or heard about it occurring with Hornady brass, I suppose it could happen to any brand, but perhaps Hornady brass has thinner case walls. While never mentioned by Salazar, my guess is that the dents in the case shoulder were caused by escaping gas from the ruptured case wall.
 
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Its supposed to be, but if it was you either have a huge chamber that took up most of your stretch on the first firing, the brass was way to small when new, or what you thought was .002 was actually .005 or .006. Or the headspace in the rifle started to change, can the barrel come loose?
 
i was there when this was happening and im not saying its not a carbon ring but it only happened with what i thought was 3-5 cases but i guess it was 10 or so? rangemaster can answer that question but if it was a carbon ring my question is wouldnt it be happening with every round or just about every round?
 
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"but if it was a carbon ring my question is wouldnt be happening with every round"

Inconsistencies in case length could cause some to show problems while others don't. Not saying that's the case here.
 
Neck is not properly sealing the chamber , possible reasons are too low a charge, some object interfering with the neck sealing maybe a carbon ring.
Maybe some of your cases are longer than others so some make contact with the carbon ring some do not.

I would also check the headspace and bolt/receiver for proper lug contact.
 
I don't think you can even push a shoulder back .020 with the correct die for the caliber unless you trim a bunch off the case holder.
 
Rangemaster said:
This was done about 10 times in the last of 50 rounds shot. My guess the pressure was too much and needed a way to escape.
Click to expand...


The problem with the too much pressure theory is that the case is 100% supported in that location, and there’s nowhere for that brass to go. If one were to assume that headspace was correct, why would that part of the case split in a perfect 360 around the case? It wouldn’t, excess pressure tends to deform the case head, because there’s a lot of unsupported brass there. If all the cases have had the same number of firings, it’s very common for the weakest to give up the ghost first, but the others are usually right behind it. I’d inspect that batch of brass for others that are about to separate.
 
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Check for donuts: Can you drop a bullet easily through a fired case?

Was the ammo wet?

Measure the case head just above extractor groove. How much larger than new brass is it? If it’s .003” or better there’s a pressure issue.

How long is the brass?

Regardless of the issue causing the problems the brass is likely junk. You’ll have to use a borescope or a piece of wire to see for sure.
 
@Praeger called BINGO. OP needs to double check. The case separated first and foremost. The dented neck is an after effect due to not enough pressure to seal the neck. There is enough pressure that it will take the path of least resistance. Also, if true I would scrap the whole lot of brass as overworked. A nice clue is the fact it started occurring well into shooting session. It would be best if you can examine all the brass from that session and look for early signs.

Oh, and now that you know you have carbon built up might as well clean it. It is possible it was caused by this phenomenon. Can't say it is isolated to Hornady brass but I'm always leery of suspicious-but-charming packaging to catch the consumer eye.

With all that said it is important to listen or double check what the OP said. What he says he is going to do is the thing to do. Thanks for sharing.
 
Last edited by a moderator:
Rangemaster said:
We bored scoped my 6cm and it had a pretty bad carbon ring. The brass was not the issue, as it was doing it to at least 10% of the brass in the last part of my match. This started about 50 rounds into the match. I just ordered some bore paste so going to try new brass and a good scrubbing.View attachment 6903945
Click to expand...
What was the problem and fix for this issue. Having the same problem out of the blue. I have changed nothing but suddenly this happens every so often
 
smoothy8500 said:
Case separation due to excessive sizing or poor quality brass. The dents are from gas pressure escaping the ruptured case.
Click to expand...
I’ve only had one separated case head and the shoulder was dented as well.

In my case the cases had a ton of firings on them and I should have retired them previously.

If your first firing really stretched the cases or you size them excessively your brass won’t last long.
 
My experiences with case head separation have always happened at high pressure. Wether it was do to over sizing or poor brass can also be a factor. It never happens in a low pressure caliber or subsonic round. High pressure can also be directly related to carbon ring.
 
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