.308 AR - Weird Brass Markings

[speeddreamz]

Recently put together a Ma-Ten upper/lower with a fulton armory barrel and BCG (headspaced by them), and while adjusting my PRI gas block I noticed some weird brass markings. I am using some dynamit nobel 7.62 nato ammo.

The case has what appears to be 2 sets of perforations(like a perforations on your common pay stub) running vertically starting from the neck of the case. It only happens after shot, not when I load a round and eject it without firing.

If I can provide any more info please let me know.

 

[cal50]

Re: .308 AR - Weird Brass Markings

Dragging on barrel extension / lugs during ejection?

Try firing a single shot and have the bolt / action stay closed then slowly eject by hand and have a look-see at the case.

 

[BCP]

Re: .308 AR - Weird Brass Markings

Feedramps on mine were a bit sharp, made marks on the necks for the first couple hundred rounds. Is that what you are talking about? Sorry can't see anything in your pics...

 

[koodbe]

Re: .308 AR - Weird Brass Markings

Looks just like my new Lilja, the barrel extension lugs are definitely the culprit.Time for some chamber detailing.Add in excessive gas pressure and it will increase this issue.Im in the process of fixing the same exact issue.

 

[speeddreamz]

Re: .308 AR - Weird Brass Markings

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: koodbe</div><div class="ubbcode-body">Looks just like my new Lilja, the barrel extension lugs are definitely the culprit.Time for some chamber detailing.Add in excessive gas pressure and it will increase this issue.Im in the process of fixing the same exact issue. </div></div>

Chamber detailing?

WHat is the excessive pressure caused by? I am in the process of adjusting the gas block to get it to shoot my surplus ammo.

How do you fix this exact issue, and is it a dangerous issue or something that will cause increased wear?

 

[speeddreamz]

Re: .308 AR - Weird Brass Markings

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: BCP</div><div class="ubbcode-body">Feedramps on mine were a bit sharp, made marks on the necks for the first couple hundred rounds. Is that what you are talking about? Sorry can't see anything in your pics... </div></div>

Updated pic, so it will go away after a while?

 

[CanSniper]

Re: .308 AR - Weird Brass Markings

It's pretty common. When the shell hits the chamber extension lugs as it is being ejected it marks the brass. You might be able to tune some out with the gas block. Or if it really bothers you, you could try to GENTLY round the Sharp edges on the two suspect lugs in the chamber. Mine does the same thing, and when I run the brass through my full lenght die it smooths out enough I don't worry about it.

 

[BCP]

Re: .308 AR - Weird Brass Markings

I wouldn't worry about that.

 

[Rando]

Re: .308 AR - Weird Brass Markings

most people deal with it. its the fingerprint of gas 308's. nothing negative causes it, and has no ill affects on the gun. after you've built enough of these you learn to soften the 4+5 o'clock lug edges before you install the barrel....if it bothers you just remove the barrel and "carefully" deburr and knock down the sharp corners. yours don't look bad *speeddreamz. i've seen them soo sharp they've pierced the shoulders on brass. good luck-

 

[matt2143]

Re: .308 AR - Weird Brass Markings

I had the same issue with most of my ar10 builds, follow the above if you feel you need the brass to look pretty after firing otherwise brass is softer than steel and will never be a negative effect.

 

[McGuyver]

Re: .308 AR - Weird Brass Markings

I had the same issues on my AR-10. The lugs and feed ranmps on the barrel extension are still fairly new and are sharp. Someone here mentioned deburring the 4 and 5 o'clock lugs. I would have thought it would be the lugs in the 3 o'clock position due to their relation to the ejector. Am I missing something?

 

[Rando]

Re: .308 AR - Weird Brass Markings

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: McGuyver</div><div class="ubbcode-body">I had the same issues on my AR-10. The lugs and feed ranmps on the barrel extension are still fairly new and are sharp. Someone here mentioned deburring the 4 and 5 o'clock lugs. I would have thought it would be the lugs in the 3 o'clock position due to their relation to the ejector. Am I missing something?</div></div>

it may be the 3-4 position. i was just working off memory.

 

[alnkal00]

Re: .308 AR - Weird Brass Markings


I have a MATEN with a 18.5" FA barrel and Im running a JP Adj gb and a Tubbs CWS (heaviest) and a Tubbs flatwire/Enidine shorty/UBR & regular DPMS BCG.

I was having the same thing happen until I installed the Tubbs CWS/flatwire.
Problem solved. Now she is very gentle on brass

I was able to completely dial her in to a point that there are
no more visible marks on spent casings anywhere.

I now have to spin the spent casing between my fingers to feel where the ejector grabs the rim because the marks are barely visible.


AL

 

[powderBurnz]

Re: .308 AR - Weird Brass Markings

Its normal, will go away after awhile.