Carbon ring on shoulder

JonathanK

JonathanK

New member
I have noticed with one of my 6ppc barrels that the carbon ring will move down the neck a little each firing untill there is a carbon ring on the shoulders. I have measured my fired brass and my loaded rounds and all seems good. I have set the barrel back shot it without roughing or polishing and I have polished it with 1000 grit. I have changed bullets powders and everything I can think of and I still get the carbon on the shoulder after 5 or 6 shots on new brass. I shoot a .269 neck with 29.7 max load of 08 133 and 30 max grains of XBR. One thing I must mention is it has been HOT here in Texas 100+ everyday but I dont get this issue with other barrels that were setup the same way this one is. Have any of y'all experienced this issue? Any ideas or suggestions would be greatly appreciated.
JCK
 
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I am amazed that there hasnt been even one response.
Maybe this has escaped notice.
 
Carbon on neck

Since you indicate it happens with repeated firings my guess would be the brass is work hardening and may need to be annealed. - nhk
 
Thats kind of what Im thinking but after only 4 or 5 firings thats pretty quick to work harden. Im gonna try annealing the same brass and see if that helps.
 
Jonathan,
I had asked a similar question here and the advice that I got as well as the explanation is as simple as nhk gave. work hardening causing the blow-by. I did anneal my brass and after the first firing there was a ring around the neck about 1/4 way down. Second firing the nice sine wave came back. It took about 15 firings for my 30br to do have the blow-by, but it happened.
I am using .004 neck tension and bump after each firing .0005 to .001.
Mike
 
I wounder if there is more to it than this?
I usually shoot a group of 50 cases over a 6 match period and never have this problem. But then as you said it is just this specific set of brass. Have you tried some new brass from another year or lot? Were the results the same.
 
I have had this happen, generally not with new brass. Also have noticed it more with some barrels. I don't think its the brass as much
as the barrel. It could be one that just needs a faster powder to make the case seal. Very light loads can do it as well as say
4350 in a 222, just to slow for the case. A well worn barrel may still shoot, but may not develop the same starting pressure, therefore
a poor seal.
 
Bob Kingsbury said:
I have had this happen, generally not with new brass. Also have noticed it more with some barrels. I don't think its the brass as much
as the barrel. It could be one that just needs a faster powder to make the case seal. Very light loads can do it as well as say
4350 in a 222, just to slow for the case. A well worn barrel may still shoot, but may not develop the same starting pressure, therefore
a poor seal.
Click to expand...

That makes sense to me, Thanks for the info!!
 
This can happen when the neck portion of the chamber has a finish issue. This makes it hard for the neck to seal at any pressure. Compare the neck area of the chamber to another chamber that doesn't seem to have this problem with a bore scope. Maybe you'll find the answer there. Just because you have polished it with fine grit, there could be something remaining that was too deep to remove without taking out more metal than desired. On the other hand, too fine of a finish will not seal as well the micro sealing rings left by the chamber reamer.

Michael
 
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Thanks Mike I will take a look at with a bore scope. What type of finish do you do on your chambers? Also, are you going to the Nationals this year in Midland?
 
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