Insipient Casehead separation?

[Zipperhead]

I apologize for the quality of the photos. I am limited by my abilities and equipment. I do not pretend nor want to be a photographer nor am I equipped as such.

Though not new to reloading/handloading, my experience with insipient case head separations and the signs has been limited. I had a military LC79 match brass case head separate once in a bolt action after 6 or seven firings. I had missed the signature "bright band" on that particular case. The band was much wider than what is shown in these pictures.

Am I correct in that these cases appear to be indicating insipient case head separation?

The two cases on the right actually have a pronounced, narrow ring that appears to be a crack. These cases have only been fired two times. The second firing was after neck sizing.

The load: Winchester case, WLR primer, 45.0g IMR 4064, Hornady 168g A-Max, C.O.A.L. = 2.800", Trimmed after first firing to 2.005".
My Hornady manual has no data for IMR4064, but my Speer manual indicates 45.0g to be a max. load. I worked this load up from staring loads over the last few months and it shoots 1.1" groups at 200 yards in my gun, so I have come to like this load very much.

These cases are from a new bag of brass. Is it possible this lot of brass is thinner, stiffer or otherwise different than the previous bag? They are different lot numbers (I checked).

Your comments are appreciated very much!

Thanks,
Zip

[WhiteTiger]

My older Hornady book shows 42.2 grains of 4064 as a max load for their 168 hpbt. Edited to add> the same book shows 43.5 as max for their 165 spire point. Both loads are with a 22" bbl model 70.

From the pictures I'd tend toward saying you don't have an incipient separation problem so much as a bright ring left at the end of contact of your backed off sizing die. With you being nearly 3 grains above the hornady load max I'm suspecting you have very slightly bulged the case head walls.

Since these suspect cases shouldn't be reloaded anyway in the interest of safety, I'd suggest sacrificing a couple of them to the hacksaw. Cut the case head vertically dead center through the primer pocket and look at the radius of the case head just at and above the point it blends into the sidewall of the brass.

If you have separation developing you will notice a band of stretched and thinned brass on the interior in that area. The inner surface of the brass where it is thinned will have a "micro alligator hide" look to it resulting from slippage of the crystalline planes of the metal.

Short of the autopsy, there is no way to say for sure, but since you aren't likely to feel safe loading these again anyway, not much is lost in expending the effort to section a few of them for inspection.



Tiger

[clytle374]

Have you tried to feel it from the inside with a hooked pick? You could cut one length wise to get a better look. I had a die that was scuffed up leave a line that looked like that on my brass, I polished the die a bit and the line went away. I had already crushed 30 rds with pliers when I figured it out.

Did your case head separation hurt the gun or you?

Good luck, I'm having brass fears myself.
Cory

[Grumulkin]

The idea of feeling with a hooked pick is good. I use a large paper clip which I straighten out and bend the tip to 90 degrees and use it to feel for the start of a groove or a crack on the inside of the case. Of course, if if there is actually a crack on the outside of the case, then it's case head separation.

If you're getting case head separations after only 2 firings then either your rifle has a headspace problem, the case has been excessively sized or your load is too hot. I've frequently found loads in at least the older Speer manuals to be a bit robust; my 308 Win. load is one or two grains of IMR 4064 less than yours.

[Archie]

As mentioned, hacksaw one in half on the long axis and look.

If that is an overload, you obviously need to back off a bit. Is the velocity showing about what one would expect, or is it going too fast?

Also, are you full length sizing the case? It is not hard to bump the shoulder back a few thousandths when resizing, which in effect makes excess headspace. Check a couple with neck sizing only, and be sure not to touch the shoulder. See if that cures the problem.

[Sunray]

Your picture gives the thousand words nicely.
Having a ring isn't terribly unusual, unless you can feel the ring with a finger nail. I'd check how far down the sizing die is. If you're loading for a semi-auto, the sizing die must be either a full length die or a small base die. Neck sizing only will do for a bolt action. The bottom of the die should just kiss the shell holder with the ram all the way up.
You're load is very close to the max of 45.9(compressed) for commercial brass with 168 grain bullets using IMR4064, on Hodgdon's site. Milsurp brass(That's likely what you're running into) is a bit thicker than commercial brass and you need to reduce the loads by 10% and work up.

[Zipperhead]

(Archie):

Also, are you full length sizing the case?

No. Neck sized with RCBS neck die.

(Sunray):

Milsurp brass(That's likely what you're running into) is a bit thicker than commercial brass and you need to reduce the loads by 10% and work up.

No. New, unprimed commercial Winchester.

(Grumulkin)

If you're getting case head separations after only 2 firings then either your rifle has a headspace problem, the case has been excessively sized or your load is too hot.

Headspace problem and excessive brass worked ruled out because 2nd firing necksized as described below and have not had similar indications in past with any brass. Previous case head separation mentioned in OP was many years ago (15ya,+/-)with LC79 Match brass that had been fired 6 or 7 times. Too hot is possible, I suppose.

(clytle374)

Did your case head separation hurt the gun or you?

No. I didn't even know it had separated until I ejected the casehead only! I had my cleaning kit with me at the time and a brass brush on the cleaning rod from the muzzle easily removed the remaining piece of the case from the chamber.

Please consider:
1) This is only TWICE fired brass.
2) First firing was new, unprimed, full length re-sized brass.
3) Second firing was NECK SIZED with a RCBS neck sizing die - not a backed off FULL LENGTH die.
4) Chamber fit was typical for neck sized cases. Easy fit with lightly snug pressure at bolt lock.
5) The cases in the photos are also neck sized after the second firing. They have NOT been tumbled. They have been trimmed and that is when I noticed these suspicious marks.
6) This load (second firing) was fired over my Chrony Beta Master.
10 round string: Hi = 2776, Lo = 2731, Avg. = 2753 fps, ES = 45.0, SD = 16.6
7) Primers appear very normal without excessive flattening.
8) Case heads are not expanded more than .001"
9) My Speer #14 shows 45.0 gn max., Nosler #6 shows 44.5 gn max., Barnes shows 43.0 g. max., Hodgdon 2007 Annual indicates 45.9 gn max. for 168 gn Sierra HPBT and 46.3 gn max. for Hornady 165 Gn SP. Only difference with the Hodgdon 2007 recipes is the primer. Hodgdon used Federal 210M and I used WLR.

I like the performance of this load in this rifle. It regularly prints 1.1" 5 shot groups at 200 yards. That's right. 200!

I sincerely appreciate all of your comments. I'm still scratching my head, though. And I hesitate to continue to use this load without getting this figured out.

Thanks again,

Zip

[Archie]

I think you should take your own advice and try another brand or - at least - a different bag of brass. See if that does any good.

If you still get the ring and separation, probably need to reduce the charge and find another load giving good accuracy. Or - put up with the short case life.

Still in all, any load that causes case separation in two loadings is not quite right. Even putting up with the short case life will not protect your rifle from the cumulative effects of overloads. The rifle won't blow up in the popular sense, but headspace can be affected over time. I would also think the chamber throat and leade may be eroded prematurely as well.

One last thought; 4064 is a fast to moderate burn rate powder. Have you considered a slower powder instead? That might gentle down the combustion process and ease the problem. Or not.

[243winxb]

On the first firing the round had excessive headspace. The load was to hot. The case was damaged then. They will come apart on the next firing. http://www.brownells.com/aspx/NS/Gun...305&mc_ID=2019 Read the part about "Sizer die setting for minimum headspace"

[Zipperhead]

Ok, I cut two of the cases down the middle. One with the pronounced ring that appeared to be a crack, and one with the shiny ring only.
The cracked case failed and broke at the crack within a few strokes of the hack saw. The other case, when cut clear through, exhibits textbook thinning of the case at the web-body juncture.

The cases have definitely been stretched.

I then dug out my RCBS Precision Mic to get some dimensions. Following the instructions sheet, I was able to determine the headspace dimension of this rifle is 1.6364". SAAMI min. = 1.6300" and SAAMI max. = 1.6400". The measured dimension falls within SAAMI specifications. That leaves the possibility of significant over-pressure situation.

Digging through the brass drawer, I found 14 new, unfired cases still in a bag... with the same lot number! I measured all of them at the case head and averaged the dimension, then measured 10 of the fired cases for case head expansion. All measurements were with a micrometer capable of .0001" measurements. Average measured casehead expansion was .0008". (The five cases exhibiting stretch marks and the cracks were included in the 10 fired cases). Apparently, overpressure may not be not the cause.

Again, after scratching my head, I measured the new unfired cases with the Precision Mic to see what the dimension was to the datum line with the cases unmolested. They ranged from .002" to .006" less than the SAAMI minimum headspace dimension of 1.6300". Such a small sample size is not a statistically significant indication of a particular lot's characteristics, but out of the 68 cases I had used in my test loads, after two firings, only 8 cases exhibited thinning rings and only 2 cases showed the hairline crack ring.

All of the above data and observations lead me to the following suppositions:
1) Though the 45.0 gn of IMR4064 is a maximum load, it may be a contributing factor, but does not appear to be the sole cause.
2) New, unfired cases were being stretched with the first firing, as much as .0116" lengthwise to fill the chamber if the shortest case was .006" shorter than the SAAMI minimum. This is significant.
3) With the variation of the datum dimensions of the 14 new, unfired cases, it is possible the five cases of concern in this thread MAY have stretched even more than the .0116" noted.
4) Adding the worst case scenario of maximum case stretching and the possibility of riding the high end of the pressure spectrum, maybe all possible negative factors occurred with these particular cases.

Finally, I have decided to set this lot of brass aside, at least for now, and utilize either once fired Hornady or Federal cases, of which I have at least 100 each, while inspecting cases closely for signs of insipient casehead failure. If the signs reappear with the different mfrs brass also, then the brass is unlikely to be the culprit. If the signs do not reappear, then the brass may the problem, but, maybe not.

Any input from fellow handloaders that can set me straight or confirm my suspicions, is very much appreciated.

Thanks,

Zip

[Archie]

Start with new cases. Fireform the cases to this chamber.

Use any old bullet and a starting load, but seat the bullet out so it engages the rifling - this insures the case head is tight up against the breech face and no possibly movement in the chamber. Just shoot them, don't worry about accuracy or velocity or anything.

When reloading those cases so fireformed, do not full length resize. Simply neck size being careful not to bump the shoulder. Use your favorite load and see how that works.

If that solves the problem, then somehow you had a functional over headspace problem. Not to say the chamber is wrong, but the cases might be too short as loaded. Sometimes dies resize too much.

[WhiteTiger]

I didn't see any mention of what these rounds are being fired in. It would help narrow down the possibilities to know what sort of action we're dealing with here.



Tiger

[kelbro]

2) New, unfired cases were being stretched with the first firing, as much as .0116" lengthwise to fill the chamber if the shortest case was .006" shorter than the SAAMI minimum. This is significant.

Would the case stretch? Wouldn't the shoulder just blow out?

Do you have access to either a go, no-go, or field gage?

[WhisperFan]

All measurements were with a micrometer capable of .00001" measurements

Don't mean to pick .... but I think you have one too many zeros.

.001 is "One Thousandth" of an inch, sometimes called a 'thou'

.0001 is "One Ten-Thousandth" of an inch, sometimes called a 'tenth'.

I have never seen, nor heard of, a micrometer that reads in "Hundreds of Thousandths" of an inch .... and I've actually worked in machine shops before.

So - this brings into question your measurement of:

Average measured casehead expansion was .00078"

That measurement (.00078") is 7 tenths and 8/10 of a tenth .... or 78 hundred-thousandths of an inch.
If, however, the measurement is actually, .0078" (assuming your mic reads in tenths) then your measurment is 7 thousandths and 8/10 of another thou .... in guns, .007" is a lot. and .0078" is nearly .008"

Just food for thought.

[Zipperhead]

Whisper fan: You are indeed correct!
I stand humbly in typograhical error.
Thank you very much.

White Tiger:

4) Chamber fit was typical for neck sized cases. Easy fit with lightly snug pressure at bolt lock.

Bolt action - Lightly used Remington 788 to be precise. I apologize for any confusion.

Zip

[WhiteTiger]

Heh... it was a bit confusing, since any locked breech reciprocating action has a bolt that locks

The 788 is a good stout little action (I've owned two of them), but being a rear locker the nature of the beast is that it is subject to more transient deflection under high mechanical load. The long, interrupted column of that two piece bolt can endure many times as much deflection as can a conventional mauser pattern front locker.

This has it's pluses and minuses; on one hand it offers an added safety margin if pressures go too high, but on the other hand high pressures can cause just the sort of mystery symptoms you are encountering.

Now knowing that you are dealing with a 788, I'd suggest as a next step having a good close look at the multiple locking lugs both in the action and on the bolt, and check closely for any signs of metal upset. Use as much magnification as you have available to do the examination.

Also I'd suggest checking the internal case volume of the lot of brass that is exhibiting the problems and contrasting that with other cases that have been through the rifle without problems. Your near top load coupled with heavy brass could easily be pushing the pressures into "oh &%$" territory.



Tiger