What would cause this on my brass?

[rhinoortiz]

Curious what would cause this? It's like a step in the should to neck area. This is once fired brass out of my brother's Scar 20s in 308win. We are going to test some loads in it and noticed this when cleaning the brass. When sized it mostly flattend back out but not completely. It does chamber the round and it does fit in my case gauges. Will this cause a problem or since it's being used in the same rifle am I good. I'm sure the brass life will be shorter.
PXL_20250809_155347673.MP.jpg PXL_20250809_155343626.jpg PXL_20250809_155401010.MP.jpg

[the_tunaman]

First thought would be headspace… second would be the chamber itself. Do you know the background on the rifle?

Doesn't look like anything to be overly concerned about, as long as they fit the go-no go and chamber fine.

Are you reloading for that rifle? If so, they should be formed to fit and it should be a non-issue.

[rhinoortiz]

First thought would be headspace… second would be the chamber itself. Do you know the background on the rifle?

Doesn't look like anything to be overly concerned about, as long as they fit the go-no go and chamber fine.

Are you reloading for that rifle? If so, they should be formed to fit and it should be a non-issue.

He bought it new. Only 200 rounds through it of new in box Fed GMM. That's what this brass is from. This is our first round of reloads for it but want to make sure this is not going to be a problem. It fits and chambers so guess we will see what happens.

[the_tunaman]

Should be fine, and optimal if those are dedicated to that rifle. Each rifle has some minuscule idiosyncrasies, which is why I keep my brass segregated for my two different Swedes and Swiss K31’s.

Brass is really forgiving - the forces it is subjected to during detonation is incredible, and the liquefaction and reformation is a miracle in itself.

[Grendel Guy]

I see your problem, you drink cowboy Kool Aid.

[4DSJW]

My WAG is that the brass was fire-formed to the actual shape of the chamber.

[hermosabeach]

Have you run a paperclip down the inside of the case as a feeler?

straighten a paper clip, use pliers to bend an L at the tip that is .20" long.

feel down the brass. Is the inside smooth or are there raised lips or nothing abnormal?

[Spyder]

I'd consider sending the rifle back.

[five.five-six]

I'd consider sending the rifle back.

sounds like a lot of troubble. should just send rifle to me and I will dispose of it properly

[ar15barrels]

Curious what would cause this? It's like a step in the should to neck area. This is once fired brass out of my brother's Scar 20s in 308win. We are going to test some loads in it and noticed this when cleaning the brass. When sized it mostly flattend back out but not completely. It does chamber the round and it does fit in my case gauges. Will this cause a problem or since it's being used in the same rifle am I good. I'm sure the brass life will be shorter.
PXL_20250809_155347673.MP.jpg PXL_20250809_155343626.jpg PXL_20250809_155401010.MP.jpg

The step between the neck cylinder and the shoulder angle is a chambering defect in the barrel that fired those cases.
FN likely does not intend brass to ever being reloaded after being fired in that barrel so they won't consider it a defect.
Only a reloader who wants to re-use the brass without extra damage need be concerned.

[Sailormilan2]

I’m not sure what we’re supposed to see. If it’s the slight step at the neck, AR15 Barrels probably has it right.
It looks like the case mouth is a little rough. That’s somewhat normal. However, if you’re going to reload the case, you need to resize the case, measure its length, and then trim it if necessary. New brass tends to stretch more upon first firing. A lot of it is due to the factory applied crimp, which comes out during firing.