Case head separation

I would not call that a separation. I had that happen with a .257 Roberts I reloaded for. I got a fine crack about halfway around the case. I did not even notice it at first. A semi is more brutal at extraction. I had just reloaded the cases too many times. I had about 100 rounds loaded and fired them off with out a problem, but they were not blown out like that.
What JamesK he is referring too is a semi-auto being "Out of time" and he is right, it will affect the brass in that way. Cutting down on the gas will tame down the extraction some, but will not solve that problem. Anyway, it is probably just the brass. One of the reasons I quit buying "Once fired brass".
 
Color me slow tonight but I just want a clarification. You loaded the case once and fired it with no problem and then you loaded it again and the second time YOU fired this piece of brass you had the problem correct?
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Yes that is correct. I bought a batch of once fired LC12 brass...x1000.

I know it isn't a chamber issue or headspace. Mainly because I have hand loaded and fired over 2500 rounds through this gun. In fact this gun has never fired factory ammo in its life. Also, I would expect a chamber issue to appear more than once in 2500 rounds.
This is also a known load of mine using the same components.

What baffles me a bit is that there was no indication of an impending crack, I know the ring test, I don't use a paper clip, I use a dental pick set I have (better than a paper clip). I checked the 2x fired cases and the other cases I fired with this one....No remarkable thinning above the web.
 
"...my headspace gauge..." That's a case gauge, not a headspace gauge. Headspace is a rifle manufacturing tolerance ONLY. Cases do not have headspace.
Your 41 grains of IMR4064 is the start load. Actually .5 under current minimum. Isn't 2400 fps either. Close though.
Anyway, as mentioned, that isn't a separation. Just normal case stretching.
"...When you buy "once fired" brass, it's..." Usually milsurp that was fired out of MG's. MG's are hard on brass.
 
Your 41 grains of IMR4064 is the start load. Actually .5 under current minimum. Isn't 2400 fps either.
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Lake City is 7.62x51 brass...Thicker with less case capacity. The maximum load in Lake city brass out of a 16.125" barrel using IMR 4064 and a 175 gr SMK is about 41.6 according to QL. The velocities as tested by my chroney are very close...+/- 25 fps in QL vs. Actual results. In .308 brass the max load is almost 44 gr and out of my gun I get about 2510 fps using Federal Premium brass and otherwise all the same components.

But this thread isn't about 7.62 vs. .308 brass/ chamber so I'll stop here.
 
But this thread isn't about 7.62 vs. .308 brass/ chamber so I'll stop here.
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There is a chance this thread is about reloaders that do not have there minds made up. I suggest someone do a review covering the sequence of events that cover case head separation. Again, I am the fan of reducing case travel, I am not in the habit of talking it to death. I determine the length of the chamber from the shoulder to the bolt face. I have purchased 1,000s of cases that have been fired in trashy old chambers, I measured the length of the cases at the range before purchasing them. "WHY! ?" I have cases that are too short from the shoulder to the case head, in an effort to reduce case travel I have to know the length of the chamber before sizing.

I do not get into the politely correct 'bumping' of the shoulder, I adjust the die for minimum full length sizing.

I do have a chamber that is .016" longer from the shoulder to the bolt face than a minimum length full length sized case; for that one I adjust the die off the shell holder .014". The .014" give me the magic .002" clearance, it does not matter to me where the clearance is, the clearance could be between the shoulder of the case and shoulder of the chamber, the clearance could be between the case head and bolt face. A reloader should understand the importance of the location of the clearance.

F. Guffey
 
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I can add in that I have had that happen, it was mil surplus chambers.

There never was a indicator with the paper clip thing, they just cracked.

I fire those gun specific cases now. The chambers were not SAAMI, they were we want these guns to work regardless of the blood the guts and the mud.

Maybe doesn't help but the wisdom about the paper clip can be wrong.

They were consistent , half split as was mentioned, no damage.

I do check the length to the shoulder and bump em back on all of them now as well.

I accept the chamber for what it is and work around it.

Those cases won't fit in any other gun but they don't have to.
 
Update

So I fired the remaining 55 rounds from that batch and inspected each case and used a dental pick to check for a thinning ring. I found nothing remarkable. I suppose I'll just chalk it up to one bad case and not worry about it. (1/200)

No need to change any of my methods seeing as how this is the first cracked casehead in this rifle in over 2500 rounds, and the first I have ever seen as a reloader in tens of thousands.

However I did turn the gas down to its lowest setting and the rifle functions fine, so I'll probably keep it there
 
Mississippi, did you happen to chronograph any of the loads after you changed the gas setting? I would be curious if there is any measured difference.
 
I did,

But I already did a test on adjusting gas system on my 556 Varmint rifle. From setting 3 - 1 it made 12 fps difference. On the .308 it made about 8 fps difference. I never tried either on "0" though which turns them into a straight pull bolt action rifle.
 
That it has such a small effect is good to know
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Ruger says that the bullet has exited before the piston begins to move.. Even if that isn't entirely true, it likely hasn't moved much at all. And the little gas chamber in front of the piston is small. So the fact that it makes almost no difference supports their claims.
 
What you had is what is generally termed an incipient head separation. They happen in degrees. If your lot of brass all has the same load history and firing history, this is a common sign you are overdue to dump the brass lot, as it generally starts happening in a number of cases. But this particular case isn't known to share the same chamber history as its brethren. It may only have been shot once in a fully automatic weapon that was a little out of time. Less likely, but possible, is it could have undergone multiple reloads if it came from a public range. Either way, the dental pick should pick the problem up if you have another one somewhere in the lot. Unfortunately, that means going through the whole lot.

Once-fired brass quality depends on the source. If they get if from the military as scrap brass, then you can be pretty sure it's not previously reloaded. The fact it's all the same year and make suggests that is the source. Brass from public ranges typically has mixed multiple headstamps.

You can section the case to get a better look at its interior condition and maybe section a random sampling of others, but I'll warn you it's time consuming to make a clean job of it.
 
Thanks Nick.

I will check each case as I prep them. Like I said before, I checked the others that I had fired and couldn't get my 45 degree dental pick to feel a thin spot. Perhaps there was one on this case but I didn't check before hand.

So, my plan is , as I go through these cases over the next few years, to pick each one and discard any that are suspect. It seems for now that there are likely not very many in danger of separation, but since it happened once within this batch, it could happen again. And if I check them in small batches it won't be a big deal.
 
Mississippi,
This won't make sense to 99.9999% of people that read this...

When the brass slug (cup) is formed into a 'Case' shape, the press MUST keep the brass MOVING, and moving the brass at a consistant rate. Some people call this the 'Drawing' process.
Constant pressure until the case body is formed to full length.
ANY change in pin ram speed or pressure will cause 'Rings' of softer or harder material.
The bigger change in ram pressure, the larger difference in 'Hardness' of the brass case wall, the reason virtually all cases are full length annealed after basic forming, annealed to minimize the variances in grain structure.

Military cases were never intended to be reloaded, so this annealing to 'Half Hard' often isn't done, the same reason the military cases are often annealed farther down the case sides past the shoulders than civilian brass...
The WORST thing that can happen in a military firearm is the shoulder/neck separates and jams the weapon!
(Used to be a common problem right up through Viet Nam, believe that or not!
Mostly solved by switching from mechanical forming presses that relied on a big fly wheel to high pressure hydraulic presses)

*IF* the press stops or 'Hesitates' during the forming stroke,
(Low hydraulic pressure, inconsistant lubrication, scratches or gouges in the dies, ect')
The brass develops a 'Ring' in the forming.

I know this since I started with a punch press when I started forming brass, and the press 'Hesitated' at first and formed the rings...
VERY hard to detect those rings without cutting the case and Rockwell testing the entire side of the case,
But you wind up with a super SOFT spot (where the press stopped) in that ring...

The brass is VERY HARD from the extrusion process, with a soft ring all the way around the case side, the two different chrystlline densities don't get along, and the cases will seperate, usually very cleanly.
(Stretched cases from overpressure or excessively long chambers usually separate jaggedly, looks like a tear)

A stretched case will develop a divot, a detectable ring/groove BEFORE they separate,
A press hesitation ring won't develop that groove or divot ring, they just separate.

Does this make any sense? Not sure I'm explaining it coherently...
 
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Does this make any sense? Not sure I'm explaining it coherently...
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Yup, i understand completely. In summary, when cases are formed, brass case hardness can be affected in specific areas of the case that are supposed to be hard by hiccups in the drawing process. The areas with different hardness do not hold together as well to areas that are much harder than they would if the case was more uniform down near the head.
Civilian brass helps correct for this issue by annealing the entire case at some point just after the drawing process...Military brass (like Lake city) doesn't. This isn't an issue to the military as they only intend to fire each case one time, and it is very unlikely to fail on the first firing. But it may fail on subsequent firings where Civilian brass would not.

And, this issue cannot be identified by a pressure ring or thinning spot in the brass, only by rockwell testing the case.

Furthermore, the hardness difference may not be a uniform ring, but rather softer on one side.

So, it could happen to one single case in a lot of brass, such that the lot isn't bad, but a hesitation in drawing on one case where their wasn't enough lube in the machine, or a slight power surge etc..

Does that sound about right?

It also happens with bullets...According to Bryan Litz, that is how bullets can have different ogive to tip lengths or bearing surfaces. If there is more lube when being pressed into shape, the bullet goes in a little deeper and if it is dry, it doen't go into the mold as far and thus two bullets from the same exact lot have slightly different bearing surface lengths or boat tails etc.
 
Sounds like a Don Meredith thing; "If ifs and buts were gifts and nuts we all would have a Merry Christmas.

F. Guffey.
 
Forming presses have to deal with hydraulic pressure, that means bypass valves.
Anyone that's worked with a bypass valve knows exactly what that means...

The old flywheel mechanical pin presses were the worst about drawing brass, just slop in the thousandths range in the crank assembly would give you fits!
 
I know I'm late to the party , but

It came sized and capped.
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No body seemed to catch this . So the case could have been fired in a generous MG chamber "THEN" FL sized to SAAMI minimum which could have been a shoulder bump of as much as .012+ . You then fired it with what would almost surely be excessive head clearance the first time so now this case has likely been stretched excessively twice . Once when it was originally fired from factory and again when you fired it after it had been FL sized for you .

I never buy already sized cases unless it's new . I don't even want my LC brass cleaned or deprimed . I want to see it in it's true once fired state and remove the crimp my self . This insures to me they are in fact once fired .

Putting all that aside I think Unclenick hit on a good point and that's the fact you really don't know the history of that piece or even that lot of brass . It very well could have been reloaded several times .
 
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