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Posted: 9/12/2020 2:43:54 PM EDT
So I got a brand new chrome lined barrel, the first chrome lined barrel I've ever owned.
There's weird looking marks on the brass. It looks like stretch marks. The little marks running the long way parallel with the case. What are they and are they normal?  Attached File |
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Posted: 9/12/2020 2:45:55 PM EDT
[#1]
Rough chamber
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Posted: 9/12/2020 2:51:22 PM EDT
[#2]
Definitely not normal.
Clean your chamber and polish with JB Bore paste. Retest If still scratching, polish with 1,000 grit wet/dry sand paper. |
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Posted: 9/12/2020 3:14:23 PM EDT
[#3]
I have a flexhone tool, would that work?
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Posted: 9/12/2020 7:45:54 PM EDT
[#4]
Fpni
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Posted: 9/12/2020 7:48:42 PM EDT
[#5]
Quote HistoryQuoted: I have a flexhone tool, would that work? @thorn653 Hold up Whats your function like? ETA Or how about the general everything about the setup |
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Posted: 9/12/2020 7:58:48 PM EDT
[#6]
Quote HistoryQuoted: @thorn653 Hold up Whats your function like? ETA Or how about the general everything about the setup Have a Superlative Arms AGB and running through a YHM Turbo. I did end up taking some Flitz polish and a chamber mop very slowly and it got rid of most of the lines on the cases now. But there's still some up front closer to the neck. I just don't want to over do it and mess it up. It functions fine, just never seen this on any of my other AR's. |
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Posted: 9/12/2020 9:13:55 PM EDT
[#7]
I would stop now unless you're planning on excessively reloading the brass. The friction of using it will clean-up all but the worst barrels and over polishing could lead to premature throat erosion.
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Posted: 9/13/2020 1:38:05 AM EDT
[#8]
If you are seeing deep extractor marks on the brass as well, thats your carrier group prematurely unlocking while the brass is still gripping the walls from pressure. Eliminate that before you go doing anything else that you cant undo. With an AGB, im guessing you have it tuned well already so,
 hope everything smoothes out
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Posted: 9/14/2020 9:35:16 AM EDT
[#9]
I agree that it is from a chamber that is not well polished. Each of my 5.56 chambers leave their own unique marks on the brass. The low-end barrel on my last build leaves marks much like the ones shown in the OP. So far, it has not been an issue either firing or reloading the brass. Cosmetic more than anything.
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Posted: 9/14/2020 2:28:57 PM EDT
[#10]
As others say, cosmetic and likely will wear in with time. Though being chrome lined, might take a little extra time; but not long.
As to the brass, you can still reload that if you want to - that's not going to cause any problems. Though, if you have any steel cased ammo; I'd run that for the next few hundred rounds. |
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Posted: 9/15/2020 5:45:05 PM EDT
[#11]
I think I am getting the same marks on my brass.
From one of my 6920’s  Which supposedly have chrome lined barrels. The black mark is from a sharpie marker stripe I put on the cases while they are still on the stripper clips. Makes it easier for me to pick up MY brass when I am done shooting. You can just barely see the dent from the ejection port or brass deflector. |
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Posted: 9/16/2020 6:24:53 PM EDT
[#12]
Quote HistoryQuoted: I think I am getting the same marks on my brass. From one of my 6920's https://www.AR15.Com/media/mediaFiles/369122/49ABE0FE-6785-429B-B3C1-203F5E51A769-1593186.jpg Which supposedly have chrome lined barrels. The black mark is from a sharpie marker stripe I put on the cases while they are still on the stripper clips. Makes it easier for me to pick up MY brass when I am done shooting. You can just barely see the dent from the ejection port or brass deflector. 
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Posted: 9/16/2020 6:25:51 PM EDT
[#13]
Quote HistoryQuoted: As others say, cosmetic and likely will wear in with time. Though being chrome lined, might take a little extra time; but not long. As to the brass, you can still reload that if you want to - that's not going to cause any problems. Though, if you have any steel cased ammo; I'd run that for the next few hundred rounds. @lazyengineer Would the steel case "polish" the chamber quicker than brass cased ammo? |
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Posted: 9/16/2020 11:33:24 PM EDT
[#14]
Quote HistoryQuoted: @lazyengineer Would the steel case "polish" the chamber quicker than brass cased ammo? Maybe. Aluminum probably would, but to be honest, I'm just not sure with steel. I don't see it "polishing" much less than brass though. |
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