Help Needed with Brass Scarring

General Firearms Reloading & Ammunition
1

I’ve got a new LMT upper that’s scarring on the necks of the brass. It happens every single round. It’s two marks on the neck that start with a gouge and then shallow up. You can feel the cut with your fingernail.

I checked the chamber with a light and I can’t see any burrs. I’m not having FTEs. Rounds that are manually cycled through the gun do not show the same marks. I can’t feel any sharp edges on the feed ramps.

I have some measurements I made with my calipers, but I can’t seem to find them right now, so I’ll post them if needed.

I wouldn’t care as much if I didn’t reload, but I’m thinking this will seriously affect the life of the brass.

Any ideas?

2

Are you using steel magazines? Any chance it could be caused by the feed lips?

3

Happens with all mags. This brass was fed from a 20-RD PMAG. I get the same result with 30-RD PMAGs and USGI mags. If it was the mag, wouldn’t it make the same mark when manually cycling rounds through the gun?

4

Its normal I have 3000 brass cases from my LMT every one shows those 2 little marks. I don’t think it comes from the chamber but they are formed from ejection from the case being pushed against the barrel extension.

5

Ahh, good to see I’m not the only one! Does it affect the life of the brass?

6

I am looking at 100 re sized cases right now it very hard to see the marks after resizing. I don’t think it would have a negative impact on case life.

7

Ok I was a little bored this morning.
I pulled a apart an unfired case and smoked the neck with a candle then dropped it in the chamber by hand then released the bolt with the bolt release.Ejected case shows 2 marks on the neck approximately .138" apart it is from the barrel extension and not the chamber perfectly normal. Feel free to check your self:happy:

8

It from the case neck hitting the locking lugs on the barrel extinction when ejecting. It’s perfectly normal and nothing to worry about.

9

Very helpful. I measured that my marks are .142 apart.

Thanks all! As always, a very knowledgeable and helpful group of folks here at M4C.

10

Ignore it and load away. You’d be surprised at some of the majorly fuX0red up brass I’ve revived and got back into service… run over smashed, etc.

11

I had the same problem on my barrel with the gouges. it turned out to be a burr on the barrel extension lugs. after removing the burr the gouges were gone and only a faint rub mark was on the case.