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Smoke
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Strange case peening
Apr 19th, 2019 at 11:33pm
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Pictured below is one of a few cases that have started peening when I fire them.  The cases have been fired multiple times in this rifle but the problem has just appeared.

Caliber: .32-40
Bullet: 175 gr spire pt, 10:1 (breech seated)
Powder: 13.8 gr 4227
Primer: Win lge rifle

Now, for some reason, a dozen or so of them (out of 100 cases) are getting peened dents below the rim.  One of the cases has actually showed some peening at the mouth, but the others are getting dented below the mouth.

I would appreciate some suggestions as to why this might be happening.

Thanks
  
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marlinguy
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Re: Strange case peening
Reply #1 - Apr 20th, 2019 at 11:44am
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Are you sure you wipe all the lube off the cases before firing? Looks like what I see when lube is trapped upon firing a cartridge.
  

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ratseye
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Re: Strange case peening
Reply #2 - Apr 20th, 2019 at 12:00pm
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A good friend used to ask "what was the last thing you did before it stopped working?" It applies to everything. So did you change anything? Marlinguy has a good point about lube and dents. Seems a little too perfectly formed but that would be my guess as well. ratseye
  
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rgchristensen
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Re: Strange case peening
Reply #3 - Apr 20th, 2019 at 12:25pm
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    The usual deformation is a wrinkle -- these are caused by a pressure wave reflecting off the base of the bullet, and getting in between the case and the bbl.   Dimples such as you are seeing are unlikely from this cause  unless the very mouth of hte case is harder than the rest of it.
      Can it be that a residual powder grain gets trapped there and is fired by gases leaking back past the case mouth?

CHRIS
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Schuetzendave
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Re: Strange case peening
Reply #4 - Apr 20th, 2019 at 5:32pm
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As you increase your powder you can get enough blowback that forces gases around the case mouth.

Some soultions are:

1. Use a lower powder load.
2. Anneal your case mouths so they will seal better in the chamber.
3. Slightly bell the mouths so they seal in the chamber before firing.

With my .32 RKS it would dimple my cases when I shot 13.1 grains of H108 pushing a 236 grain bullet.
I stopped this from happening by reducing to 12.8 grains of powder but then found out later I had better accuracy at 12.4 grains.
I believe your load is too hot.
« Last Edit: Apr 20th, 2019 at 6:54pm by Schuetzendave »  
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Smoke
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Re: Strange case peening
Reply #5 - Apr 20th, 2019 at 7:21pm
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Sounds like some good advice.  I'll play around with them and see what happens.

Thank you all!
  
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Schuetzendave
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Re: Strange case peening
Reply #6 - Apr 20th, 2019 at 8:11pm
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I checked all my loading manuals for using 4227 in a .32-40.

The majority of powder loads for using 4227 in the .32-40 were for JACKETED BULLETS only.

The only powder load to use 4227 with a LEAD CAST BULLET was maximum 13.0 grains with a 196 grain bullet and 13.5 grains for a 204 grain bullet.

I assume your 10:1 is your alloy mix which is too hard and will allow gases to cut around the bullet.

For breech seating we usually use alloys between 30:1 to 20:1.

I use 20:1 which softens over time from aging.
« Last Edit: Apr 20th, 2019 at 8:17pm by Schuetzendave »  
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Smoke
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Re: Strange case peening
Reply #7 - Apr 20th, 2019 at 8:32pm
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Oops, I wrote the alloy ration wrong.  It's more like 90:1.  Very soft, perhaps even pure lead.

I didn't cast these, I got them from a friend and was just using them for offhand practice. 

Ordinarily I shoot 30:1 and don't have the problem.
  
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JWDreamstone
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Re: Strange case peening
Reply #8 - Apr 23rd, 2019 at 5:26pm
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I found that Peening will happen when You use stainless pins for tumbling when You use the same brass over and over.  the pins will cause tiny dents in the brass and upon Firing The micro dents pop out.  Do you use pins to tumble or was the brass used
  
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Smoke
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Re: Strange case peening
Reply #9 - Apr 24th, 2019 at 1:09am
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The cases were tumbled, but that was three rounds of shooting ago, and I use ceramic media.

Those cases will get shot twice more over the weekend during the San Diego ISSA Regional match.  I'll report back if the peening continues.

Thanks
  
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JS47
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Re: Strange case peening
Reply #10 - Apr 28th, 2019 at 11:20pm
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A tip I got from Ken Lewis is to wipe the chamber with a patch on a short cleaning rod after each shot. If I don't do this some times I will get a deformed case like you show after firing due to some residue left in the chamber.

JS

  

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