Case head separation
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Thread: Case head separation



  1. #1
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    Case head separation

    What is your process you use to avoid case head separations? My Marlin bolt action in .308w has only neck sized cases used in it after the first firing. Those cases have been trimmed and annealed twice. I have reloaded those cases to the point that I am about to break down my loaded rounds and begin anew with better record keep for every new bag of 50 winchester brass I open. Seeing how I neck size only, what would you watch for on a case needing discarded? How many loads near max are you getting with neck sized only brass? Has anyone here had a case separation? details?
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  2. #2
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    First off, how many times has that brass been loaded? Have you check for incipient case head separation using a hooked paper clip? If you did and felt no groove in the brass and the primer pockets are still reasonably tight then that brass should be good to use some more. The following is something I wrote up and posted in another forum which they added as a sticky. You can use is as is or with a neck sizing die. Even so, with neck sizing you need to do a full length resize every now and then. Ss a matter of fact, using these instructions may negate the need for neck sizing entirely. My loads are just as accurate by this method as when I neck size. The main thing with this system is to push the shoulder back only the minimum amount necessary for smooth easy chambering.

    This is how I set up my sizing die for bottleneck cartridges.

    1. Take a once fired factory case from your rifle and blacken the neck and shoulders with a Magic Marker or Sharpee pen. Some people like to smoke the neck and shoulder, but I find the Magic Marker/Sharpee pen a bit better.

    2. Carefully lubricate the case.

    3. Loosen the lock ring on the sizing die and back off about two turns from when the die is set to touch the shell holder.

    4. Size the case. Note where the marks are on the case and turn the die down about a half a turn and size again. Turn down some more, and resize again. What you are looking for is the marks on the blackening just touching the shoulder.

    5. Clean the lube from the case and try it in the rifle. It may chamber just a bit on the snug side. If so, turn the die down ever so slightly, lube and size again. Wipe off the lube and try in the rifle. If it slides in as easily as a factory round, you should be good to go. If not, usually one more very slight adjustment should fix the problem.

    6. Tighten the locking ring for the die and you're done. You have just set your sizing die up for a custom fit to your specific rifle, rather than a generic one size fits all guns.

    Paul B.

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  3. #3
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    A quick note from a guy who has a comparator and precisely measures the process.

    If one is trying to dial in precise case fit with just enough shoulder setback to allow free chambering without setting it back excessively, the die must be adjusted in very small fractions of a turn.

    Right from the start.

    The die threads are very coarse and a half turn represents a big difference in die and case shoulder movement. Keep in mind we are adjusting in about 0.002” increments where one increment means no effect and the next increment is ideal.. 0.002” movement is a small fraction of a turn of the die. Again, reckon the coarse threads.

    A gage or comparator lets one dial in the process exactly and provides much more information as to correct adjustment than not measuring what you are doing. “Feel” is often unreliable.

    Not really contradicting anything said earlier, as methods may vary, just reiterating that due notice should be made that this exacting adjustment is best quantified and carefully crept up on. If you want to know if you are getting the precise amount of shoulder bump, best measure to see if what you think might be happening is actually happening.
    Last edited by 35remington; 07-12-2019 at 07:18 AM.

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  5. #4
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    To nail down just how elusive O.002” is to obtain accurately by turning the die, it is about 1/36th turn of the die.

    That is a ninth of a quarter of a turn. Another reason I say that if you want to know how much you are moving the shoulder, you have to measure IF you are moving the shoulder or not, and if you are, just how much you are moving it.

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    I was completely unaware of that method of resizing but I look forward to attempting it in several calibers. However I don't know if my 1 1/2" grouping deer rifle will benefit or if it is more for the true accuracy shooter. A cartridge having a true fit to the chamber if achieved would be an improvement I am certain, but I am most likely the weakest link with the rifles I shoot.
    In a 7mm08 rifle I used once fired Hornady brass then neck sized only ( I am not sure of how many firings- my poor record keeping is something I am about to completely turn around) and I found the separation beginning to occur just below the line of the neck. It was so bad that in an inertia bullet puller the cartridge separated. Any idea what was the cause?

    I am aware of the paperclip and watching for a bright ring on the case but in a neck fired on shoulder bumped only case how do you proceed with saying enough is enough with a particular piece of brass of the whole lot?
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    I agree with 35Rem. I have had target guns and wildcats that I set dies using milled surface on top of press to set the bottom of the die with Mics. Having said that it's going overboard on most of the rack rifles. I inspect and measure my brass after cleaning. In 30/30 I have never had signs of head separation. This is usually visable as a line, sometimes perforated around the case right above web. On LV cartridges I've never got to anal on keeping records on times loaded. Most of these cases I loose are to neck cracks. The 30/30s are always FL sized because I usually have several rifles in that cal. I have 3006 GI match that was 1x when I got it. It's been loaded 7 times. Trimmed once and not annealed. This brass is for an original Win 1895 and the loads are mild. On belted mags is where case life shows up the most for me. The smaller the bore the more the effect. I get about 5-8 out of them with full magnum loads. It also depends on the brass. Remington brass seems to be harder and will show signs earlier. Federal is not bad and Win seems to be the best. It's copper content in the brass that has a lot to do with case life. I have Norma 357, 44mag bought new in 60s that has been loaded unbelievable times. Also 222 Rem and 257Robt that have been run through at least 10 times. Don't really know because back then I didn't worry about such things.
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    The sizing method is mostly to ensure you do not have a die/rifle combo that is a mismatch of too much die sizing combined with a chamber with the shoulder too far forward. It is less an accuracy thing than a case life insurance step.

    Those that happen to have a good match are unaware of this procedure...they just crank the die down as far as they can and load away. Most do not load enough to know if their method of sizing affects case life or not. That don’t know/don’t care methodology does not work with some of my dies, but then I am paying attention. The idea is to figure out just what you have, and worry about it if it matters.

    If the case indicates good health it is okay to keep loading it, but if max loads are all you do there is good sense in not overdoing it. I shoot so many less than full powered loads that cases demoted from full power use still get used.

    For obvious reasons a case failure with full power loads is not a great thing to have happen. Especially when it matters. Do not try to get all you can from something that has a finite lifespan. Exact numbers are hard to express, but the older a case gets the less confidence you should have in it.

    When it separates it will do so just above the expansion ring of the case.
    navajo and Ojaileveraction like this.

  9. #8
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    You could also use the Redding competition shell holder set. 5 shell holders that go up in 2th increments 2 - 10 th over size. Start with the largest (10th) and work down until the case just fits. Use this with the case neck Die as well and you will also resize the same amount of case neck getting the same neck tension all things being equal. Just keep a note of which shell holder you use per rifle. Gar.
    graymustang likes this.

  10. #9
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    I adjust sizing dies in 1/24 turn increments, mainly because it is easy to accomplish and duplicate if your press has a hex nut on top. This amounts to .003" of adjustment.

  11. #10
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    Use an RCBS case mic here. Simple to use (read) for precise measurement of headspace, and COL. Agreed most of the rack rifles don't gain much if anything from this level of precision, but on those rifles that do really shine with this attention to detail, along with longer case life in most cases. Use the rule that the when a batch of cases requires their fourth trimming, they get thrown away at my house, not the range, as someone may scrounge the cases and load them even more.
    rob42049 likes this.
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