Incipient Case Head Separation

Discussion in 'Handloading and Reloading' started by Walkalong, Nov 7, 2013.

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  1. Walkalong

    Walkalong Moderator Staff Member

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    Folks ask about how to check for the internal signs of impending case head separation and what it looks like from time to time so I thought I would post some pics. A buddy brought me some .308 brass he had shot a time or two too many.

    I have posted this printed pic I did in paint before showing the internal rut with the tool for feeling it. It has a couple of "feelers" laid on it.
    Case Head Separation Check.JPG

    Some people like to shoot brass until it shows the bright ring on the outside, and some just shoot it until a crack happens. I would say that is firing the case too many times, but some folks do it.

    Case head separation happens when we fire a case over and over and when it has room in the chamber to stretch. If a rifle has excessive mechanical head space a case can do this on one firing. Another way is if we push the shoulder back way to far and create "artificial" headspace, or excess clearance in the chamber. It adds up to the same thing. The case has too far to stretch and it thins near the case head.

    When we fire a bottle necked rifle round the firing pin pushes the round forward until the shoulder stops the round in the chamber. Then the pressure blows out the case to fill the chamber. The softer front of the case grips the chamber walls sealing off the hot high pressure gases from blowing out of the rear of the chamber. The harder thicker case head holds pressure in the rear. This is most important job of the brass, to contain the gases/pressure and hold together during firing. The brass case, with help from the chamber walls and breech face, seals the open rear of the chamber, and forces all the gas forward down the barrel.

    When fired, the softer front of the case is gripping the chamber walls, while the harder rear of the case which expands minimally is free the move rearward to the breech. This cause stretching of the case, normally right where the thicker web transitions into the thinner wall. It stretches because the front of the case holds tight to the chamber wall while the rear does not. It slides to the rear until the breech face stops it.

    This is why we do not want to over size, or push the shoulder back too far, on our cases, as it will increase how much the case stretches each time and lead to failure sooner than necessary. We can use a case gauge like those from Wilson, or various tools to measure how much we move the shoulder. Ideally we want to move the shoulder .003 or less.

    This is a case with a shiny ring. It showed up as a dark line in the pic, but to the naked eye it is a bright line, the one we always talk about.
    Rut in Kent's .308 Case #1 Pic 1.JPG

    Here is the same case cut open to show the internal rut we are feeling for.
    Rut in Kent's .308 Case #1 Pic 2.JPG

    Here is another case he shot until it split, almost in half. Cutting it too close for me.
    Rut in Kent's .308 Case #2 Pic 1.JPG

    Here is that case cut open to show the rut. You can also tell where it is split all the way through on the right side.
    Rut in Kent's .308 Case #2 Pic 2.JPG

    Here is a pic with a feeler tool shown inside. This case head almost separated. Bad Ju Ju.
    Rut in Kent's .308 Case #2 Pic 3.JPG
     
    Last edited: Nov 15, 2016
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  2. Walkalong

    Walkalong Moderator Staff Member

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    Using a case gauge to adjust a sizer.
    Wilson .223 Case Gauge Pic 3.JPG

    Using some other measuring tool to control how much we move the shoulder. there are a lot of options here. Mine is home made.
    308 Shoulder Gauge Pic 3.JPG

    Comments, additions, pics?
     
    Last edited: Nov 5, 2016
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  3. jwrowland77

    jwrowland77 Member

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    Thanks Walkalong. Very informative. Very nice.

    I always run the paperclip inside after resizing, but never know if there is an indention or not. Most feel like glass and smooth even after firing them 3 times already.

    Does the indention feel scratchy, or can you definitely tell that there is a definite "dip" in the case wall?
     
  4. ReloaderFred

    ReloaderFred Member

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    Walkalong,

    That's probably one of the best illustrations of case head separation, and impending case head separation, I've seen. This can also occur in bottleneck pistol cartridges such as the 357 Sig and 9x25 Dillon. The 9x25 Dillon is especially prone to this and I usually limit my brass in this caliber to four loadings.

    Thank you for making this clear to those who are less experienced than some of us.

    Fred
     
  5. Walkalong

    Walkalong Moderator Staff Member

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    You can definitely feel it when it gets to the point it is a problem. Practice on cases and then cut them open to see what you are feeling.


    Thanks Fred. :)
     
  6. 12guns

    12guns Member

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    Good info, thanks. Do you know how many loads he got out of those before they crapped out on him?
     
  7. blarby

    blarby Member

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    "Things that should be in the loading library of wisdom"

    This
     
  8. TexasShooter59

    TexasShooter59 Member

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    As for scratchy or smooth, I have noticed that some makes of cases seem to feel one way, and other brands might feel differently. Regardless of the rut.

    I have set a few cases aside that I wanted to investigate internally, but I have never read how to cut these open. I'm sure there are preferred methods (without using a machine shop). How did you open up those in the photos above?

    Thanks for posting this topic.
     
  9. jwrowland77

    jwrowland77 Member

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    A dremel works great on cutting cases, don't ask how I know, I just know. Lol. :D
     
  10. Mohave-Tec

    Mohave-Tec Member

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    I have and use case gauges for everything. I check even once fired brass regularly. Still, after I fire a hand load made from once fired brass I toss that brass in a twice fired bin of that caliber. So far, I've never reloaded a case a third time. I would, and I will, I just haven't gotten to any of it yet.
    I really do enjoy the process of assuring my hand loads match my chamber dimensionally.
     
  11. Mohave-Tec

    Mohave-Tec Member

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    Walkalong, I'm from South Georgia originally. Where do you find room to stretch out some longer shots in Alabama?
     
  12. Lee S. Forsberg

    Lee S. Forsberg Member

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    Very good pics!! As well as a very good explanation.
     
  13. Jesse Heywood

    Jesse Heywood Member

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    Jeweler's saw works for those cuts.
     
  14. Rule3

    Rule3 Member

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    Thanks for the excellent write up.

    Is the case head separation directly related to how "Hot " the loads are.

    I would image that loading at the max loads would decrease the number of times a case can be loaded? or does it occur regardless, just by using the same case)s) too many times?
     
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  15. Walkalong

    Walkalong Moderator Staff Member

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    Those were opened up with a grinder and the rough edges cleaned up. Keep water handy to cool the case.
    Max vs light will definitely make a difference. The difference between max and near max is probably not much, but I don't know for a fact.
     
  16. oldpapps

    oldpapps Member

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    My complements. Excellent presentation.

    Thank you,
     
  17. higgite

    higgite Member

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    Thanks for the timely (for me) refresher, Walkalong. The pic of your homemade h/s gauge also rekindled a project for my lathe. :)
     
  18. moxie

    moxie Member

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    Nice job Walkalong. Thanks.
     
  19. Walkalong

    Walkalong Moderator Staff Member

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    No, but neither does he. I still haven't talked him into letting me help him reset his sizer.
     
  20. TNBilly

    TNBilly Member

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    Rule3 - Case stretch is more related to difference between the case size and the chamber than the hotness of the load. Any usable load will pretty well stretch the case to form it. Cases usually stretch at "about" the same point, just ahead of the web and will do so accordingly to how much headspace the individual case has in the particular weapon. Usually a unfired factory case will have in the area of .006 headspace, though I've seen some of the rimmed mags with as much as 18-19 thou. If you were to size a case all the way back to original size each loading - in my experience you'll start seeing case failures in the second to third firing for regular cases and in the case of the mags sometimes the second. This is why anyone loading rimmed magnums reloads setting the headspace to the shoulder, not the rim as the factory does. There's no absolute with case life, annelling every second loading certainly helps out a lot with neck life and doesn't take that much of your time. That's my 2 cents........
     
  21. ATLDave

    ATLDave Member

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    Man, what a great set of posts, Walkalong! I am in your debt.
     
  22. Rule3

    Rule3 Member

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    Does this occur more often in certain calibers than others. Say 223 vs 308?

    What about in bolt actions where neck sizing only is done more so than full length.? I understand the case expands and relaxes either way.

    I clean all my cases and look them over of course,but now I need to stick a probe in everyone?

    Clean, Size, trim, de- bur chamfer, case head checking, no wonder I shoot more handguns;)
     
  23. A Pause for the Coz

    A Pause for the Coz Member

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    Sticky!!!!!!!
     
  24. Walkalong

    Walkalong Moderator Staff Member

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    It doesn't care what kind of gun, although there is more stretch to some actions than others. It is directly related to how much the case has to stretch each time it is fired. That is determined by how much clearance, or head space, the cartridge has each time it is fired. Headspace is a static measurement mechanically built into a gun (Datum point to breech face), while clearance is how much slop or extra space from the flat of the case head to the breech when the case is fully forward against the datum point in the chamber. I often times call it "artificial headspace". We create this by pushing the shoulder back too far. We create an unsafe "headspace" condition in a gun where the mechanical headspace is fine.

    Expanding side to side to grip the chamber walls does not hurt anything, it is when the rear of the case moves backwards to the breech face while the front stays put gripping the chamber walls. The middle has no choice but to stretch, and where this generally shows up is at a point near where the thick wall near the web tapers down to the thinner wall just above the web.

    Neck sizing does not push the shoulder back, so case stretching is kept to a minimum, just like it would be if we measured where the shoulder is and size it (Push it back) minimally.

    We exacerbate the stretching problem when we move the shoulder back too far for the gun it is fired in.
     
  25. dagger dog

    dagger dog Member

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    Great info from a very knowledgeable source !

    May I add, rimmed cartridges fired in firearms with out of spec chambers and ones with head spacing problems suffer the same effects.

    Loose primer pockets (that's why priming by hand is preferred by some) can be a sign of pressure worn and headspace problems which cause the separation too.
     
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