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Question time again. I am shooting a W/Weaponry AR , 7.62 x 39, and just started seeing some odd scratches on the brass rim and body. The scratch runs from the rim and is noticeably deep, as in a little metal displacement, then tapers off as it runs up the body about .3" to .5" in a diagonal direction at first. As the scratch tapers off it also straightens out fwd to the mouth of the case. I replaced the extractor a while back but I don't think this is causing it as the scratch is travels fwd of the rim. I checked for corresponding wear marks on the magazines, one new and the other used ASC 10 rd. mags, and there are none. It appears that the lug in the barrel (feed ramp?) which engages the bolt at 6:00 position is causing the scratch. Looks like there is some metal transfer there but is tough to tell. Straight as the brass first contacts the lug and then spiraling as the bolt rotates during engagement and lock up. Most noticeable on Herter's ammo but also occurs on Winchester, PPU and Hornady brass. I am burning some steel case ammo through hoping it might dress down a possible burr on the lug. The scratches wouldn't be an issue except I reload and the scratch in the rim keeps the resized case from dropping in the case gauge unless I dress down the displaced rim mat'l. Also I have concerns about the body scratch being a stress riser causing premature cracks.

 

I have some pics attached of the brass and wonder what everyone's input might be.

 

As always may God bless and guide us all.

 

Matt

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You can lightly touch up the feed ramp and lug edges to cut that sharp edge off. Just knock off the high spots...don't get all crazy :laugh:

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I'm just curious. Do you get the same scratch if you chamber a round and manually extract it without firing it?

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I'm going to try that tomorrow. I'll keep you posted.

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So...I took a needle file and dressed the feed ramp with a dozen or so light strokes. No real noticeable material removal as seen through my reading glasses. After inspecting the fired brass it appears to have helped some. Still scratching but the length is shorter and still displaced mat'l on the rim. If I chamber a round using the mag and bolt release and then manually extract the brass still scratches. If I place a round in the chamber by hand and the release the bolt there is no scratch on extraction. Looks like the feed ramp is the issue. I'll dress it down a little more and see what happens next week. Only thing that bugs me is why the scratching started all of a sudden. I did have an extractor break and wonder if the chip damaged the ramp.

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I had a barrel that did that. I used a Krated insert in a Dremel to knock the edges off.

 

Kratex is like a hard pencil eraser with see diamond abrasive in it. It's pretty handy stuff.

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Break the sharp edges INSIDE and OUT on the feed lips on your mag. This will help to some degree. I also go in and round the BACK edges of the lugs on the extension lightly. This helps somewhat. If I have a donut/helper on the extractor spring I pull that I use them on very few up my bolts.

 

Greg

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Man, I knew I came to the right place! I will use all the suggestions. My ejector did not come with the o-ring from Windham so I don't have to remove it. Looks like I may have to remove the barrel to get at the barrel extension lugs better. Wish the garage had AC.

 

Matt

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I just reach back into the extension with my Dremel and a long Cratex cylinder to break the edges. It takes very little to make a difference.

 

Greg

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Cratex is one of the wonders of the world. Have several from coarse (kind of coarse) to extra fine. If the OP goes Cratex, make sure you get the lesser "Rubber Abrasive", not the "MX" for that particular task (imo) unless you really know what your doing. Grit is up to you. https://www.cratex.com/gunsmith-tools-supplies/CRATEX-Products-for-Gunsmithing

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I just reach back into the extension with my Dremel and a long Cratex cylinder to break the edges. It takes very little to make a difference.

 

Greg

What color / colors would you suggest on the extension?

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Gray last time. Hose the thing down with brake cleaner when done.

 

Greg

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Woooo Whoooo! Looks like polishing up things is doing the trick. Still some extremely light scratching that I'll address with the cratex when I can borrow some from work.

 

Thx and God bless.

 

Matt

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Who says Okies and Texans aren't neighborly? (VBG)

 

Greg

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Hate to admit it but I was born in CA. Really not my fault as dad was career A/Force. Spent time in Norman. OK but anything in the Rockies is home. Maybe someone is hiring a stove in A and P in Idaho. But as Greg implied you can expect good things from this site no matter where we're from!

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