Case Head Spearation Confirmation

[NoHeavyHitter]

Since it's 9mm Mauser, I'm gonna take a guess that you might be shooting a mil-surp rifle? Such guns often have "generous" chambers to help deal with dirt and other rigors of war.. The best way I've found to make my brass live in surplus guns is to segregate it to the rifle it was fired in and use a neck-size only die. Full-length resizing often winds up over working a case. By neck sizing, you won't have to trim as much and your cases will last longer.

[Metal God]

The shoulder bump averages .003".

From what to what ? From .000 to .006 ?? A .003 bump generally will not give you case head separation in 5 loadings . If most of your cases are only .003 bump from fired size I'd start to think your chamber is also generous in diameter as well . Do you have a case gage ? If possible neck size only then drop it into the gauge . If it sticks way out of the gauge then your chamber diameter is to big and you are likely stuck with the 4 or 5 firings per case .I suggest neck sizing first because sometimes the chambers neck is the only thing that is generous and will cause the case to stick way out of the gauge as the fired case neck is to big to fit through the gauges neck . This happens with one of my rifles .

You can send a fire formed case in and have a custom die made which would account for the larger diameter and allow less working of the brass ???

[arrowshooter]

I agree with neck sizing only, but started running into stiff chambering so I took a few off the shoulder to smooth it out. I will say that I have been running the same brass in this rifle that I do in my other two which is my bad for not sizing its own case in a more timely fashion. My other two rifles have new chambers and the brass is identical for those.

Bump is pretty consistently .003" but it will spit out an occasional .002 or .004, never over that though.

I have head space gauges and still have lots of room left on the No Go gauge. As for the case gauge, I can drop a fired case butt first in an LE Wilson and it goes in about half way. All three of my 8mm mausers leave the necks fat which can be a real pain in the *** trying to perform some checks.

I am going to load up some new PPU brass and start from scratch with neck sizing only for this gun.

[J-cat]

Have you considered that line might be a tool mark from your chamber? When my brass lets go it’s about 25% of yours.

[Metal God]

I agree with neck sizing only, but started running into stiff chambering so I took a few off the shoulder to smooth it out.

To clarify , I meant to neck size only to test in the gauge not for your actual loadings . I have a 308 that fails the gauge badly and at first I thought it was do to the diameter of the fired case body . After some measuring I determined it was only the neck portion that was to large in diameter and the neck not the body of the case . The fired neck size was causing the case to contact the gauges neck area resulting in the case sticking up out of the gauge . To confirm my findings I neck sized the case and after it dropped freely into the gauge .

Have you considered that line might be a tool mark from your chamber

Interesting possibility

[fguffey]

I just wanted to confirm that what I am seeing here is case head separation. I did have one let loose yesterday which had me looking closer at the rest of the fired brass from the day

I believe you should have been looking closer at the first firing, that is not easy when you are a bumper reloader. I am not a bumper reloader because I find it impossible to move the shoulder of the case back with a die that has full length case body support. After that you past up a good chance to become a fire former.

A good fire former would have measured the length of the case from the shoulder to the case head before firing and again after firing. The before and again after helps the reloader to understand the effect the chamber had on the case when fired. I know the length of the chamber from the shoulder to the chamber to the bolt face before firing. That puts me into a different category, I form first and then fire. When I eject a case after firing I am ejecting a fired case.

And then there are those that insist on firing a case 4 times to make sure it is fully grown. To avoid that category the rfeloaders must move up beyond fire forming and bumping status.

Back to before and again after: Measure the diameter of the case head. A good number for case head expansion for the first firing with a new case from the factory is .00025". I would be wasting my time explaining cases with .005" case head expansion; but I will tell you the case with that much case head expansion if fully grown.

And then there is the PPU: I do not have one case with a PPU head stamp so I can not compare the difference between a PPU case and a good case. AND! I doubt there is a bumper reloader on this forum that would know what to look for.

And I have mentioned I have chambers that are long from the shoulder of the chamber to the bolt face, I am the fan of forming first and then firing but I have fired cases in long chamber with .127" clearance without stretching the case between the case head and case body; if shortening the case between the shoulder and case head .002" is called bumping by bumper reloaders stretching the case .127" between the case head and shoulder would qualify as 'wreck-um bumping'.

But? When I fired the cases with .127" clearance none of that happened.

F. Guffey

[J-cat]

The OP’s PPU case looks typically thinned out after 4 reload cycles.

[divingin]

I pulled a few pieces of LC 308 scrap brass that showed the separation line to take pics of the wider matte line I was talking about (post #4.) Took a few pics with differing lighting, and they all looked pretty much identical to the OP's pics. The line shows up in images as thin, well-defined mark, almost like a scratch. They appear quite different in person, to the naked eye, as the appearance is wider, and much lighter in color.

The attached image sort of shows what I was describing, but is still not as obvious as in person.

[arrowshooter]

So just now getting back to this.

I have started the process of separately sizing the brass for each of my 8mm Mausers. I have started with brand new cases that I have now fired in each rifle. I have stripped the bolt on rifle #1 and have a question: When chambering the resized brass do I want to feel any "cam over" on the bolt, or do I want the bolt to close with just the slightest "tight" feeling?

[mjmagee67]

I've had case head separation on several caliber and the line is never that defined. It's more a light colored band. You will get some thinning if you full length resize every time. If you only neck rezise I've gotten 20 reloads out of some brass. You cut away doesn't really show much thinning at the base. The paper clip method works very well you can feel the thin area pretty easily.

[Metal God]

When chambering the resized brass do I want to feel any "cam over" on the bolt, or do I want the bolt to close with just the slightest "tight" feeling?

Well that depends , lets start with you never want hard to close bolts ( cam over if you will ) . Just a hint of resistance is fine if that resistance is from the shoulder of the case stopping on the shoulder of the chamber . I mean that's the feeling you get when you neck size only so sure , very slight resistance is OK but IMO not optimal . You really want your bolt to close with no resistance especially on a stripped bolt . Now there's more to it then just that though . A case sized WAY to short from head to datum point will allow your bolt to close freely . Just because the bolt closes freely does not mean the case was sized optimally .

If you have the ability to measure the case that ( closes with just the slightest "tight" feeling ) from head to datum point , you likely would want that case sized .001 to .002 more from head to datum .

Also make sure you are trimming these cases to the trim to length . This will remove the possibility the case mouth is to long and causing that resistance .

[arrowshooter]

If you have the ability to measure the case that ( closes with just the slightest "tight" feeling ) from head to datum point , you likely would want that case sized .001 to .002 more from head to datum .

Going in .0005" increments, I found that at .002" under I could just barely feel it and the end of the bolt throw. The bolt would just drop on the .003".

Also make sure you are trimming these cases to the trim to length . This will remove the possibility the case mouth is to long and causing that resistance .

I did trim each case so I'm good there.

I'll go through this with rifle #2, load them up and go choot'um.

mjmagee67, I have definitely put the paper clip to good use and found that I could feel the thinning in a good portion of the 5x shot cases, but the resistance was greater in the cases with the "line". The case that did partially separate, did so right on that line. It's just weird. No other cases have that line, but I will inspect each one after every firing from now on.

Thanks to all and I will report back.

[fguffey]

So just now getting back to this.

I have started the process of separately sizing the brass for each of my 8mm Mausers. I have started with brand new cases that I have now fired in each rifle. I have stripped the bolt on rifle #1 and have a question: When chambering the resized brass do I want to feel any "cam over" on the bolt, or do I want the bolt to close with just the slightest "tight" feeling?

Rifle #1? Even if you only had one Mauser 8MM rifle it should not be necessary to custom size test cases for that one rifle. You have a press, shell holder and die, both with threads. Any reloaders that is good enough to shorten the case between the shoulder and case head .005" should be able to form 30/06 cases to 8MM57 cases. And then I could ask: How can a reloader that can size a case to within .002" of length between the shoulder and case head miss especially when they start with a 30/06 case.

The difference in length between the 8MM and 30/06 from the shoulder to the case head is .127" so I wonder how a reloader can miss. I wonder if a master reloader can size a case within .002" of length why cant he size a set of cases that that would measure in .002" increments from minimum length/full length size to .011" longer than a field reject length gage.

That is what I do, I take out the box of 20 cases and start chambering. I have never found it necessary to make it a ritual like removing the extractor, firing pin assemble etc. and then there are interchangeable bolts but that is for advance reloaders.

The only skill necessary for a reloader to accomplish these skills is to be able to measure the case from the shoulder/datum to the case head and adjust the die in the press to and or from the shell holder. I do find it strange all of the reloaders claim they have the skills but none of them display the knowledge.

F. Guffey

[arrowshooter]

Rifle #1? Even if you only had one Mauser 8MM rifle it should not be necessary to custom size test cases for that one rifle. You have a press, shell holder and die, both with threads. Any reloaders that is good enough to shorten the case between the shoulder and case head .005" should be able to form 30/06 cases to 8MM57 cases. And then I could ask: How can a reloader that can size a case to within .002" of length between the shoulder and case head miss especially when they start with a 30/06 case.

The difference in length between the 8MM and 30/06 from the shoulder to the case head is .127" so I wonder how a reloader can miss. I wonder if a master reloader can size a case within .002" of length why cant he size a set of cases that that would measure in .002" increments from minimum length/full length size to .011" longer than a field reject length gage.

That is what I do, I take out the box of 20 cases and start chambering. I have never found it necessary to make it a ritual like removing the extractor, firing pin assemble etc. and then there are interchangeable bolts but that is for advance reloaders.

The only skill necessary for a reloader to accomplish these skills is to be able to measure the case from the shoulder/datum to the case head and adjust the die in the press to and or from the shell holder. I do find it strange all of the reloaders claim they have the skills but none of them display the knowledge.

F. Guffey

Thank you for your input and pointing out my typo. I was adjusting at .0005" increments which is pretty easy since the dies are threaded and my calipers go that far out (though the caliper is only accurate to +/- .001").

[mjmagee67]

Have you tried just slightly bumping the shoulder back and doing a neck resize. I would be curious how far back the neck is being bumped with your full length resizing.

You should measure the length from the base to a datum on the shoulder then resize and remeasure. One would suspect you may be pushing the shoulder back close to .010 inch. or so. Which is only allowing 5 or so reloads.

If you can bump the shoulder back .002 inch to .003 inch you will get more firing. Furthermore you could try neck sizing only. I normally can get 4 to 5 neck sizing's before I will have to bump the shoulder back .004 inch or so. The bolt gets harder to close when the shoulder gets pushed out a little to far. You will probably have to anneal the necks after 5 or 6 reloads. At least that's what I have found with my 30-06 and 308. I get 4 of 5 reloads and the accuracy goes south because lack on neck tension and the bolt starts getting harder to close.