Possible carbon ring. Help interpret.

[jskmtd]

So I have about 220 rounds down my 338 lapua ackley improved. 100 of those rounds was fire forming new brass to the ackley chamber. Last outing I was seeing pressure signs and my groups opened up to about 1 moa when it had been shooting in the .3's. I have been working on the chamber at the end of the brass with a bronze brush and bore tech carbon remover. The first picture is before the bronze brush the second picture is after the bronze brush. What do you guys think? Am I getting it or do I have more work to do? Any help would be appreciated.
Thanks,
Jon

 

[Quicksilver338]

How long are you letting the c4 sit? I'll go at mine pretty aggressively over the course of a day or two letting it soak in well to the carbon.

 

[jskmtd]

I let it soak in for about 15 hours before I tried the bronze brush.
Thanks,
Jon

 

[birdiemc]

I'm interested to hear from some of the gunsmith crowd as to whether that is a carbon ring or not...to my untrained eyes it looks like a little throat erosion and a clean chamber

 

[Rick Richard]

Does not look like a carbon ring to me. Erosion or machining issue maybe?

 

[Korhil78]

If you are talking about that black line, its not a carbon ring. That's where the rifling stops and the chamber starts if I am looking at it right. My rifles have that as well. Seems that a lot of people have bought bore scopes lately and have been making a fuss over nothing. Its fun to look at though.

And to add, I am by no means a professional at this. But, Carbon rings are not going to be as nice and uniform as that. But If I am wrong, someone please correct me!

 

[LaHunter]

To me, it looks a carbon ring in the bottom photo (but I am far from an expert). Not as bad as I have seen (in my rifle), but it is there. It appears that you removed it, or just about all of it with your cleaning, but the 'after cleaning' photo is not quite as sharp as the 'before cleaning' photo. Have you shot your rifle since cleaning?

 

[birdiemc]

Korhil, I agree
It is the start of your throat. From that point to the rifling is your free bore.
I know the drawing is 338 lapua not AI, but it still illustrates what we're looking at

 

[jskmtd]

Well sounds like it is time to go shoot it and see if the pressure signs are gone and the accuracy is back. Thanks for all the responses.
Jon

 

[Mikecr]

Yeah, it's not a carbon ring or anything to be concerned about. Pictured is a mild ring forming:

 

[6.5x284tony]

That is definitely carbon. I didn't realize how real the carbon problem was until I bought a bore scope. I have since polished out several throats that look like this. They will look brand new again once they are cleaned up.

Tony.

 

[jskmtd]

I went out and shot 6 rounds of the same load that was giving me pressure signs and poor accuracy before the cleaning of the throat area. No pressure signs ES of 8 for the last 4 shots a group of just over .5 moa with the magneto speed attached. However it is averaging 27 fps slower than when I worked up the load. I will load somemore up and go test the load to see if it is shooting as good as before. Thanks for the replies.
Jon

 

[birdiemc]

I went out and shot 6 rounds of the same load that was giving me pressure signs and poor accuracy before the cleaning of the throat area. No pressure signs ES of 8 for the last 4 shots a group of just over .5 moa with the magneto speed attached. However it is averaging 27 fps slower than when I worked up the load. I will load somemore up and go test the load to see if it is shooting as good as before. Thanks for the replies.
Jon

Keep the updates coming. Very helpful

 

[StanB]

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