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Old November 14, 2006, 08:22 PM   #1
Harry Bonar
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Case Head Separation

Dear Sirs:
Hope I can attatch this?
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Old November 16, 2006, 08:44 PM   #2
Harry Bonar
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case head separation

Sirs:
Didn't get my attatchment on from floppy disk.
Case head separation simply is caused by only two things. Incorrect sizing die mis-adjustment or excessive headspace.
If it's headspace, it'easilly cured - a new bbl or set back and re-chambered.
Poor die adjustment: having the shell holder contacting the die bottom hard!
After about three firings you get incipient case head separation - after that if you keep sizing the case completely you get case head separation. Always, especially with a belted magnum after first firing headspace it ON THE CASE SHOULDER!
Harry B.
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Old November 26, 2006, 10:04 PM   #3
alexander hamilton
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mr bonar,
would that apply to autoloaders too? i full length resize all autoloader cases but i dont go all the way down to the shellholder.
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Old November 28, 2006, 12:37 AM   #4
T. O'Heir
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"...I dont go all the way..." You're not full length re-sizing. Full length sizing dies, and any other die, should be set up so the shell holder just kisses the bottom of the die with the ram all the way up. A 1/16" gap is ok.
Case head separation is caused by excessive headspace, bad brass or both. How the die is set up doesn't matter. You CANNOT adjust headspace by doing anything to the die or the case. Cartridges do not have headspace. Headspace is a firearm manufacturing tolerance. It has nothing whatever to do with the case.
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Old November 28, 2006, 11:49 AM   #5
brickeyee
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"Cartridges do not have headspace. Headspace is a firearm manufacturing tolerance. It has nothing whatever to do with the case."

But adjusting a die incorrectly can result in the combination of case and chamber exhibiting symptoms of excessive headspace even if the firearm chamber is within tolerance.
Bottlenecked rifle cartridges without rims or belts headpsace on the shoulder. That is what sets how far into the chamber the case will move.
If the shoulder has been moved back (towards the case head) to far, the cartridge will stretch on firing to match the headspace available in the gun.
A correctly sized cartridge in a chamber that HAS excessive headspace does exactly the same thing. It stops on the shoulder, then stretches to fill the available chamber.
Saying that headspace has nothing to do with the case being used is not really correct whan reloading.

You can also form cases to fire in a chamber that has excessive headspace by adjusting the die to not set the shoulder back to 'nominal' but instead leave it at (or very close) to the as fired dimensions.
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Old November 28, 2006, 09:00 PM   #6
James K
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"A correctly sized cartridge in a chamber that HAS excessive headspace does exactly the same thing. It stops on the shoulder, then stretches to fill the available chamber."

Not quite. When the chamber is overlong or the cartridge too short, correct firing pin protrusion will not allow the primer to fire unless the case is gripped by the extractor. Then the primer will fire, but the result is the same as a rimmed cartridge, the front simply blows out to fill the available space. It is that condition that can be compensated for in reloading by neck sizing only.

If a short round can fire with the base well ahead of the breech face, there will be case stretching, just as with excess headspace in the rifle.

As to headspace being purely a matter of the gun, that is not really true. The variation in ammunition is the reason why there is tolerance in headspace; if there were no tolerances in ammunition, headspace could be set to a fixed figure which would hold until wear and bolt lug setback changed it. For example, a GO gauge is used to determine that the longest case allowed under ammunition tolerances will chamber and fire. A NO-GO gauge ensures that the shortest case allowable under ammunition specs cannot stretch enough to separate. So there is definitely a relationship between ammunition and headspace.

But chambers don't change or expand (at least not to any measurable extent). What changes are the bolt lugs and lug seats, which compress and wear over time. That results in increasing headspace. When headspace reaches a certain point, it allows the rear of the cartridge to push the breechblock back far enough to cause case separation. If not corrected, the cartridge case will ultimately back far enough out of the chamber that it will have insufficient support and will blow out, wrecking the gun. And no amount of reloading care will change that situation; it will only delude the gun owner that he is "making up" for excess headspace.

Jim
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Old November 29, 2006, 02:46 PM   #7
brickeyee
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"Not quite. When the chamber is overlong or the cartridge too short, correct firing pin protrusion will not allow the primer to fire unless the case is gripped by the extractor."

there is plenty of room for the firing pin to ignite a primer with excessive slop in a rifle.


"Then the primer will fire, but the result is the same as a rimmed cartridge, the front simply blows out to fill the available space."

Not at all. The extractor is usually well forward of the correct cartridge position when the bolt is actually in lockup.
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Old December 4, 2006, 06:41 PM   #8
Harry Bonar
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head separation

Dear Sirs:
Refer to "The A-Square Shooters Manual" and study the sizing operation. This is explained rather well there.
If you totally size a fired case to factory specs (and die instructions) after about 3 to 5 shots you WILL develop incipient (or complete) head separation.
A minimum case in a maximum chamber can result in, belted magnum cases in .015 stretch! If you continually resize to die instructions about 3 - 5 times you WILL have incipient head separation.
In rechambering from 458 to 458 Lott, and deepen the belt recess you will have a blow-up. Solution - order your Lott reamer will the belt cutter removed.
Harry B.
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Old December 6, 2006, 04:49 PM   #9
Harry Bonar
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case head

Dear Compadres:
Yes, headspace is in the gun - not in the case. I agree with the statement - but, if the headspace in the gun is at or near a "no-go" reading, or even a "go" reading (that being .220 go and .224 no-go) and your case belt is only .216 (normal case actual belt size)If your chamber is .223 (which would be a safe depth) that gives a headspace in "that" particular gun - you have a heaspace of .007!
Now upon firing the case walls grab the sides of the chamber and the head stretches back .007 back to the bolt-face you have stretched back.007.
Then, if you size your case to die mfgrs. instructions you have on the next firing you get another .007 stretch you have a total stretch of .014!
Most loading manuals now, at this late date, recommend headspacing on the SHOULDER of Belted Mag cases - for this very reason
We can talk about rimless cases later - but we must understand the reason for belted Mag cases anyway - these (belted magnum) cases are not any stronger than rimless cases - as a mater of fact are the most dangerous cases to reload for not understanding these facts.
Harry B.
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Old December 6, 2006, 05:20 PM   #10
ZeroJunk
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I have full length resized many 30/06 brass ten or twelve times.I have never had one seperate.I have had two 7MM Rem Mags seperate.I had never heard of headspacing them on the shoulder until I started reading this forum.Makes sense.Thanks for that.
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Old December 6, 2006, 05:36 PM   #11
brickeyee
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" Yes, headspace is in the gun - not in the case. "

While headspace is measured in the gun at manufacture, it is just a way to standardize chamber sizes and allow any ammunitiomn of XX type to fint in any chamber of XX type.
There remains a positive tolerance on the chamber headspace and the cartridge to be fired in it. You can measure the headspace dimension on a cartridge to try and ensure that ot will fit it a correctly headspaced chamber.
Does the cartridge have headspace?
It has a matching dimension that must be less than the chamber.
Saying headspace is "not in thet cartridge" would imply the dimension of the cartridge can be set anywhere you want it.
I do not think that is what you intended at all.
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