New Grendel build dents brass upon loading

[Glock357]

I recently built a Grendel and I noticed that it consistently dents the brass case, about midway of the body, upon loading. This only happens before firing because I checked brass that was loaded into the chamber but not fired and the ding is still there. So far I fired about 200 rounds, factory and reloads with no malfunctions.

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Do you guys have any ideas what is causing this? I am worried that it weakens my brass I use for reloading.

My theory is that as the round is pushed from the magazine and jumps into the chamber the bolt pushes it on the locking lug between the 2 feeding ramps and gets dinged/dented on the sharp tip of the lug. The edge closest to the barrel of the lug between the 2 feeding ramps is very sharp.

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Does this sound like a possibility? If yes can I fix this? Can I grind down the lock lug about a mill between the 2 feed ramps and polish the edge closest to the barrel?

Now another variable is that I am using my 6.8 SPC magazines. I don't have Grendel mags yet. I tried both PRI and ASC with no difference. Could it be the magazine?

Another issue is the 2 dings on the throat of the case. I am less concerned about those because I get them on my 6.8 as well. They only happen after the case is fired when it is extracted it gets dinged on the barrel extension lock. Can this be fixed?

Could both dings be caused by the sharp inner edge of the barrel extension lock lugs?

[VASCAR2]

Most of my brass have similar dents if shot in an AR-15 and has never been an issue. Maybe someone else will chime in.

With a new rifle or mags the brass cases get a lot of scratches but with use the sharp edges wear off and the brass looks better.

[mongoosesnipe]

I use a 10rd mag loaded with 5 to avoid tis issue would fine on the bench, for hunting i use a steel grendal mags but for the sake of preserving brass on the bench mags work if loaded just a few rounds

[Texas]

Have you tried a different magazine?

[LRRPF52]

The dent on the side of the case is normal when firing, but not before firing.

You could color the area that you think is causing this, and see if the color matches the ding.

[rabiddawg]

Is it ok for the bolt lugs to mark the extension like that?

I just looked at my three grendels and neither of them look like that.

[Glock357]

Is it normal for the bolt lugs to mark the extension like that?

I just looked at my three grendels and neither of them look like that.

Are you talking about the receiver? I mated my receiver with the m4 feed ramps of the barrel extender using my dremmel. The bolt has not marked the barrel,extension.

[rabiddawg]

In the pic, it appears that the lugs on the bolt are scaring the extension where they would mate.

Fwiw, I looked at some of my brass and a few have a ever so slight dent and some has nothing. I don't sort my brass so i don't know which one may be making the dent. My dent isn't enough for me to worry about. It's more of a smudge.

[Glock357]

The dent on the side of the case is normal when firing, but not before firing.

You could color the area that you think is causing this, and see if the color matches the ding.

I just racked 2 unfired rounds made with new brass and got this. The dent is not as bad as during firing because the force of the bolt is not as large. I ll try to add some color on the barrel,extension to see if it transfers to the brass.image.jpeg

[Glock357]

In the pic, it appears that the lugs on the bolt are scaring the extension where they would mate.

Fwiw, I looked at some of my brass and a few have a ever so slight dent and some has nothing. I don't sort my brass so i don't know which one may be making the dent. My dent isn't enough for me to worry about. It's more of a smudge.

I see now what you mean. I think it's the harsh light of the iPhone flash causing artifacts. It looks better to the naked eye.

[Glock357]

Have you tried a different magazine?

I will once my new ones arrive.

[Glock357]

I did the color test by using a sharpie to color the barrel extension lock lug edges and traces transferred to the brass. I also noticed that the bullets get quite scratched up as well by the edge at the end of the m4 feeding ramps. I don't know if this affects accuracy. When I put my finger behind the edge or tip of the m4 feeding ramps the edges there feel sharp as knife, so I think I will grind slightly and polish and see if that helps.

[koden]

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If this was happening when the round was loaded you would not see it on fired brass. The pressure of firing the round would smooth that out against the chamber wall unless there is an issue with the chamber.

I think you have 2 things going on. In the pic in post #9 you are seeing a mark left by feeding. In post #1 you are seeing a dent left by extraction and the shell hitting the ejection port of the upper receiver or shell deflector.

[Glock357]

If this was happening when the round was loaded you would not see it on fired brass. The pressure of firing the round would smooth that out against the chamber wall unless there is an issue with the chamber.

I think you have 2 things going on. In the pic in post #9 you are seeing a mark left by feeding. In post #1 you are seeing a dent left by extraction and the shell hitting the ejection port of the upper receiver or shell deflector.

That's a very good point.