Case mouth doughnut

[David Christian]

@ToddKS, I have experienced a similar brass buildup in my Lapua 6.5cm after 6-8 firings. I don’t know what caused it, yet found that neck turning cleaned it up nicely. Zoom in on the attached pic and you can see how much of the lip and neck/shoulder cleaned up through skim turning. You will also notice that skimming did not cut anything from the center of the neck.

DC

 

[MikeMcCasland]

Definitely a tumbling issue. Had it myself several times (sporadically), and no longer wet tumble most brass as a result.

 

[ToddKS]

@ToddKS, I have experienced a similar brass buildup in my Lapua 6.5cm after 6-8 firings. I don’t know what caused it, yet found that neck turning cleaned it up nicely. Zoom in on the attached pic and you can see how much of the lip and neck/shoulder cleaned up through skim turning. You will also notice that skimming did not cut anything from the center of the neck.
View attachment 1114757
DC

This is what my cases looked like after turning the neck as well.

 

[Uncle Ed]

Why would tumbling cause a donut to form at the start of the case neck?

The cases hit each other as they are tumbled, and the soft annealed case mouths get hit and become peened. Meaning thicker and with a sprue like edge on both sides of the case mouth. On pistol cases when you expand the cases you will see very small brass flakes inside the case.

The cases can hit each other in a dry media separator also and can ding up the case mouths.

I have a STM wet tumbler, a Lyman vibratory tumbler and a few weeks ago I got a sonic cleaner that doesn't allow the cases to hit each other.

I have found the only way to solve the wet tumbling case mouth problem is to trim and deburr every time you wet tumble.

With a magnifying glass you can see the effects of wet tumbling, especially if the case mouths were trimmed and deburred the last firing before tumbling.

 

[rwj]

@ToddKS, I have experienced a similar brass buildup in my Lapua 6.5cm after 6-8 firings. I don’t know what caused it, yet found that neck turning cleaned it up nicely. Zoom in on the attached pic and you can see how much of the lip and neck/shoulder cleaned up through skim turning. You will also notice that skimming did not cut anything from the center of the neck.
View attachment 1114757
DC

Great picture/illustration! I tumble clean with pins and when I “skim” cut necks to address the dreaded neck/shoulder donut, material is only removed from that junction, never from where you’ve shown. My experience is with 6BR and .243 cases. Perhaps something unique to 6.5?

 

[Mikemontminy]

Looks like your using a pin gauge as a mandrel. Maybe the mandrel needs a steeper angle ground so it enters the case easier. The angle you have might be flaring the neck as it enters. Check out pictures of other mandrel from another manufacturer. You’ll see what I’m talking about. You can also cut your cleaning time way down by using boiling hot water in your tumbler. I didn’t catch what make your tumbler is. If the drum is plastic I wouldn’t go super hot with the water as it may damage it. My drum is metal with a rubber liner . I always boil the water then dump it in with the pins, brass ,dawn and lemishine. Run it for 25 minutes. The hot water cuts the cleaning time in half. Good luck Mike

 

[Brians356]

A flare at the case mouth leads me to wonder if your cases were long for the chamber, hence getting flared when last fired.
May want to check your case to chamber length relationship.

How can a chamber apply a flare at the case mouth?
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[dmoran]

@brians356
If a loaded case is near max chamber length, then when fired will grow in length a certain amount, it could make contact with the end of the chamber; hence, the chamber can/could flare it inward(attaching below an image reference):

 

[Brians356]

@brians356
If a loaded case is near max chamber length, then when fired will grow in length a certain amount, it could make contact with the end of the chamber; hence, the chamber can/could flare it (attaching below an image

Running into the chamber end would curl the case mouth inwards towards the bullet, trying to reduce its diameter. A "flare" is "a spreading outward", i.e. an increase in diameter, like a trumpet bell. How does the chamber create that?
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[Ccrider]

Running into the chamber end would curl the case mouth inwards towards the bullet, trying to reduce its diameter. A "flare" is "a spreading outward", i.e. an increase in diameter, like a trumpet bell. How does the chamber create that?
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This is what I was deducing; but, can’t you get a trumpet shape of the neck is tight and the mouth that is thinner takes most of the pressure?

 

[ToddKS]

Running into the chamber end would curl the case mouth inwards towards the bullet, trying to reduce its diameter. A "flare" is "a spreading outward", i.e. an increase in diameter, like a trumpet bell. How does the chamber create that?
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If this were what happened then when I ran the mandrel down the case mouth it would have pushed the material outward from the inside of the case thus creating the flare.

I believe my issue was driven by the wet tumbling but I know for a fact that the mandrel moved the brass outward creating the flare due to material being inside the casemouth that should not have been there. The flare was not on the cases before passing through the mandrel and not all cases were affected or affected equally.

Thinking back, I cleaned this brass in two batches. One batch did not come clean on the first pass and I ran it a second time through the wet tumbler. My hypothesis is that these are the cases that had the issue as they would have been tumbled for twice the normal time.

I am definitely reevaluating my cleaning process as a result of this experience. This was a PIA to fix. I am not ready to walk away from wet tumbling but I am looking at options to decrease the number of minutes the cases are in the tumbler. I may also try increasing the volume of water and or media to help mitigate the impact forces in the tumbler.