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Mike - give me a day to get answers to all your questions.

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Headspace - the most misunderstood term in the reloading neighborhood. Here's my take on it: You have a portion of a case called the "head" located above the rim (and belt on some cases) below the shoulder. Now, you have a "space" between this "head" and your given chamber. This space is usually tracked by head expansion of a given case, measured in .0001".

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If the above is true, you can't "headspace" off a rim. The rim has nothing to do with the head or the space between the head and the chamber. Right?? Sorry, that's a peeve of mine when I hear people talk about headspacing off a rim, or better yet the shoulder.

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“Headspace is defined as the distance from the bolt or breech face to a measuring point within the chamber forward of the breech. With rimmed cartridges, such as .22 long rifle, 30-30 or .357 Magnum, the measurement is to the front of the rim cut. Straight- walled rimless cartridges, such as .30 Carbine, 9mm Luger or .45 ACP, are measured to the mouth of the chamber. Rimless bottleneck rounds, like .223 or 30-06, are measured to a point on the shoulder at a certain specified diameter. Belted magnums, .300 Win. Mag., or .375 H&H, are measured to the front of the belt cut, essentially like a rimmed case.”

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Cartridges that headspace on the shoulder, work kind of backwards from that. When the firing pin strikes the primer, the case is shoved forward until the case shoulder hits the chamber shoulder. Then ignition happens and the sides of the case expand outward and grip the chamber walls. The rear of the cases then flows back until stopped by the breech face. Again, careful resizing of the case can minimize this.

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All that to say, that I do not think your problem is head space related. I believe it is simply a matter of over working the brass in a very concentrated area and where it is likely the thinnest. Kind of like bending a piece of wire in the same place over and over again – it breaks. Perhaps the Contender’s chamber is slightly larger around as well which would exacerbate the issue.

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but how is this different from the sharp crease at the neck/shoulder juncture of a bottle neck case that is also getting worked every time a case is resized (unless there is "zero headspace")? The only differences I can see are 1. the bottle neck cartridge is supported when the crease is formed (usually, that is... but there are dies for neck-sizing or neck with shoulder-bump that do not support the entire case the way a full length sizing die does) and 2. the bottle neck chamber is relatively closer fitting with the case-form when firing than Zigs' 41 Mag. cases are (same general shape, that is).

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From: "Michael Krall" <krallmi@h...>
Date: Thu Jul 31, 2003 4:37 pm
Subject: 41 Magnum case separation

There is a fellow on another forum (http://www.handloads.com/,
under "general discussion", thread is "case life" by "Zigsjigs") that is partial sizing with an RCBS carbide die (0.660" down from case mouth) and has had near separation on the 5th reload... a case fell
off of the bench and popped in two when it hit the concrete. He is using 50 very well selected cases and firing them in a 14" T/C contender. He is in search (successfully) of "repeatable" 1 MOA (or less) 5 shot at 100 yd. loads. A very few of the loads of the loads have been "hot" (some of which were the near-separation loads) but many are the lower pressure loads of charge work-ups. He is trimming after each firing (trimmer left set the same to clean case mouths if they grew... which most of them have throughout the 5 firings). On close inspection he has found signs of incipiant separation on 22 of the 50 (now retired). I have run this around in my brain for days now and all I have is guesses. I'd like to understand what is "real"
about this. Would you help me get "clear" on the subject, please.

Mike Krall

PS... "Jose" (can I call you Jose...?), if push comes to shove, would you permit me to "cut and paste" some of the thread I mentioned into this forum? Would it be OK with you for me to "export" from here to there (I have "OK'ed" the process with John Knuteson on the other
end)?


From: "Lloyd deVore - Canuck Publishing" <canuck@r...>
Date: Thu Jul 31, 2003 7:32 pm
Subject: Re: [JGBS' target='blank'> 41 Magnum case separation

"Yes" to both questions.

An interesting tale, too. I can see that a person might expect separations with the process as described. If the cases are lengthening with each
firing, and some is being cut off each time, the brass for the additional length must be coming from somewhere.

I suspect that "somewhere" is the point at which the die ceases to size the case, perhaps about 1/10th inch or so above the case rim. That is a "corner", so to speak, and as such is a "stop" below which the case flow may not occur.

At the time of firing, it appears the little shoulder on the inside of the case (created by the sizing down of the portion of the case above the lowest point which the die could reach), is being blown both outward to fit the chamber walls, AND forward. That, of course, both lengthens the case, and stretches it at the point where the minute "shoulder" was formed. Enough stretching and it become both thin and work hardened (brittle) at that point.

Do it enough, and "Voila", a case separation. That's one theory, anyway.

I would imagine that whether the die is carbide or steel makes little or no difference. The sharper the edge on the bottom of the die, the more likely a little tiny shoulder will be formed where the bottom of the die stops in the sizing process.

Using a cutting cloth (crocus cloth?) to round the bottom edge of the die might help in reducing the frequency and rapidity of the separations. A die
specially tapered from fired size at the base to "sized" size about half the length of the case above the base would likely eliminate most of it. That modification, of course, would be much easier to do with a steel die.

Personally, I would first round the bottom of the die, then put some crocus cloth on a high-speed rotating shank and work it in and out of the die to
try to "cut and try" making a taper in the die. It might take quite a while with a carbide die, although only the very bottom is carbide ( a carbide
ring insert, actually). Above the carbide ring, it would likely cut as easily as any other steel die.

Whadda you other guys (and gals) think?

Jose


From: Duane Mellenbruch <dmell@m...>
Date: Thu Jul 31, 2003 7:57 pm
Subject: Re: [JGBS' target='blank'> 41 Magnum case separation

I am wondering if using a shim under the sizer die, to in effect move the shoulder up or down the side of the case might increase the case life. Seems like most of the size dies reduce the case diameter down to the "web" which would be the strong point on the case.

Sort of raises the question, is "neck sizing" a straightwall case beneficial to case life? This would suggest that it is not.

Frankly, I have never considered trimming pistol cases. Well, except for the time that I erred in thinking that case length not bullet diameter was a
factor in mis-fires in a 357 Contender.

Duane


From: "Ian Foran" <iforan@e...>
Date: Thu Jul 31, 2003 9:48 pm
Subject: Re: [JGBS' target='blank'> 41 Magnum case separation

Duane,

I think carbide dies are designed to not reach the solid web, to save cracking the carbide ring.

My .41 sizing technique is to size the case until the maximum width is reduced 0.002" for reliable chambering. I've never rigorously tested the
accuracy advantages/disadvantages of this attempt at case centering, but the gun is very accurate. Almost all of the loads fired in it are stout, and my oldest batch of brass (20 years) has been retired because some of the primer pockets aren't as firm as they used to be; and I'm tempted to think that the hard necks and subsequent low neck tension is reducing accuracy?

I would bet a dollar that the case separations are a result of hard lockup and/or the idiosyncrasies of the Contender locking mechanisms? The most common misunderstanding about the Contender is that accuracy and case life are promoted by a tight case fit. Having to slam the gun to get it to lockup is
bad.

Anyone shooting a Contender should wander through Mike Bellm's site and read
the articles.

Brain dead Ian (only one cup of coffee so far)


From: "Michael Krall" <krallmi@h...>
Date: Fri Aug 1, 2003 12:11 am
Subject: Re: 41 Magnum case separation

Jose, Duane, Ian...

Thank you for thinking about this and replying. I'm going to cut-and-paste the thread from the Handloads forum when I can (the site is down right now) so that there is a more complete story than I have
provided. Also, "Zigsjigs" is working on posting some data about his "Project 41" that may provide more detailed information. Zigs may not say it, but these 50 cases of his were very carefully sorted...
by weight and volume, case wall thickness and variation, rim thickness variation < 0.0003", trimmed, in Zigs words, "ex-actly!", primer pockets, flash holes, etc. This is also his first experience
with a straight-walled pistol case although he has been around Contenders quite a bit and with the same general accuracy approach.


QUOTE:
At the time of firing, it appears the little shoulder on the inside of the case (created by the sizing down of the portion of the case above the lowest point which the die could reach), is being blown both outward to fit the chamber walls, AND forward. That, of course, both lengthens the case, and stretches it at the point where the minute "shoulder" was formed. Enough stretching and it become both thin and work hardened (brittle) at
that point.
QUOTE:


I may not have been clear enough and/or may not understand clearly
enough... He is partially sizing the case and the lower edge of the carbide ring is stopped at 0.660"... essentially "neck/shoulder juncture", and this is where the separation has occured... front
piece of case measured at 0.0659".

Mike Krall

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From: "Lloyd deVore - Canuck Publishing" <canuck@r...>
Date: Fri Aug 1, 2003 4:28 pm
Subject: Re: [JGBS' target='blank'> Re: 41 Magnum case separation

Yes, Mike, exactly where one would expect the separation to occur.

Any time one resizes PART of a case, he can't avoid forming a very small "shoulder" at the bottom of the die...i.e., just above the head of the case a bit.

When you blow that "shoulder" back out to contact the wall of the chamber by firing the cartridge, you can't help also blowing it ahead a tiny bit. That
causes the case to stretch right there at that tiny shoulder.

Causing the case to stretch also causes it to thin at the point where it is stretching, i.e., at the little tiny "shoulder" at the bottom of where the
sizing die came to on the case during re-sizing.

The more pressure you use, the more emphatically that thinning occurs. So, with hot loads, one fairly quickly can get case separations.

Three solutions. The first one only slows down the appearance of the problem. The second and third can eliminate it

1) Use less pressure, or
2) Use a marginally larger diameter die so there is less "shoulder" created
by sizing, or
3) Find a way to size down farther on the case...clear to the rim if
possible.

Jose

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From: Bob Brunjes <bob@t...>
Date: Mon Aug 4, 2003 9:37 pm
Subject: Re: [JGBS' target='blank'> Re: 41 Magnum case separation


Mike, and everyone else,

If "neck" sizing straight-wall cases necessarily causes case separation,
we should remember that full-length resizing is relatively recent to
reloading, even with straight-wall cases. For a lot of years, the Lyman
"nutcracker" (310) tool was used to load cartridges like .38 Special,
.45 Colt, and .45-70 Govt., and the 310 most specifically did *not*
full-length resize. When I started loading in the 1950's, Lyman
wouldn't even claim that the Tru-Line Junior press, which used the same
size dies as the 310, was capable of true full-length resizing.

To full-length resize, Lyman sold dies that would be familiar to later
Lee users, or to owners of Wilson case gauges. I used these in .45 ACP
and .30-06, and you banged the case into the die with a hammer and block
of wood, and then banged it out with a hammer and rod.

With all that history, I've never heard of case separation as a part of
the old reloading lore. Could it be that separation was not an issue at
lower pressures? What's different in this modern case?

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Zigs,

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What other forums besides "AR", Handloaders, JGBS?

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What was "virgin" case-head measurement?

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Where, "exactly", are you measuring the case-head expansion and what are you measuring with

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You said, "I figure virgin brass will 'set' after the first firing". Do you mean case-head diameter... say, from where the case wall starts to thin (about 1/4" in fron of the rim) and down or...?

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Have you repeated and compared any "ramps" or "accurate loads" from the "matched and partially sized" tests with the new, "un-matched" and full-length sized cases?

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