Case head failure gives me something to think about!

I was wrong/we were wrong

Well, it wasn't thinning brass, at least not the kind normally seen from stretching due to excessive headspace or excessive full-length sizing. I sectioned the case head with my band saw and here's what it looks like:

sectionedcasehead.jpg


As you can see from the arrows, and from the corresponding side, this case wasn't anywhere near the point of separation due to sidewall thinning. The case was sectioned right through the middle of the failure area.
 
Used the wrong powder on accident?
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Anything's possible, I suppose, but I fired 49 other rounds from the same box without a hint of case damage, excessive recoil, or any other signs of abnormality. IMR 4831 or surplus M2 ball (H4831) from a jug from River Valley Ordinance are the only powders I EVER load in 270, and every 270 bullet I own is a 130 grain bullet. Even if there had been a bridging in the powder measure it would have shown up as a round with powder level up higher on the neck or spilling over since this load normally fills the case up to the top of the shoulder anyway.

I paper clip tested the other rounds from this lot of brass and none are showing signs of incipient head separation.
 
There was something that bothered me about that first photo. The lower edge of the tear appeared to taper inward. Now, it is shown to be torn open at a diagonal. It ripped open as if there was a fold or flaw right at the edge of the case head, and what I'm wondering, did the expanding shell wall tear away from the non-expanding base?

Do two things for me. First, get a very precise measurement of that case head, and of the cartridges diameter up above the area of the rupture, and do it on some other cartridges from that day's shooting.

Second, you really owe it to the shooting public to contact the maker of the shells and send that in for examination. They ahve no liability, since it was a reload, but there may have been a flaw in the metal that they can find.

This really is an anomaly. I can't get a grip on what happened. I still keep looking at sizing/chamber issues, or a fold/flaw in the metal that didn't show up when the shell was drawn.
 
The primer isn't flattened bad at all but looks like a gas leak @ the 11 o'clock position? I've had ancient CCIs blow pin holes along the edge like that w/starting loads. Kinda chalked it up to stress fatigue (approx 30 ~ 40 yr old). I know, doesn't address the separation issue . . . . . I've have experienced a lot back in my less affluent days w/smoke but not major gasses/particles. Now I know it can happen
 
Well, the Remington is a stronger action, I believe. On the down side, if you blow a case head with a Remington you'll usually blow out the extractor and you're all done until it's replaced.:cool:

You're right about the case not being thinned out. That usuall occurs a little further down.:cool:
 
This particular lot of brass was bought new as a box of 100 from Midway in 1988. I'm not sure Remington could learn all that much from it.

Does brass age harden?
 
No, it doesn't. Certainly not in only 20 years, unless it was sitting in a really substandard set of conditions.

Certain problems can cause brass to become brittle and weak, particularly corrosion that breaks down the bonds of the alloy, leaving patches of copper or zinc that lack the strength of the virgin alloy.

That is what mercury primers did; the mercury would cause weak spots by breaking down the alloy. I believe, personally, that it was a vastly overrated problem, as a miligram of metallic mercury vapors vs a a heavy sheet of brass should be negligible.

I really am at a loss on this one. I'm not ashamed to say it. There just doesn't seem to be an obvious smoking gun, and all of the evidence I see just doesn't seem to point to any single thing. No matter what happened, brass is elastic, and should not have torn like that, and your brass, from what I can see, is still clean and undamaged alloy.

You would expect to see this in badly corroded ammunition, ammo that had deteriorating powder, steel shells, cheap brass, extremely old brass that had weakened and damaged alloy, and other various circumstances that would have weakened the brass of the walls badly.

A case rupture like that is one of the least things you would expect from an over pressure. that is the strongest part of a shell except the web, and it is backed up by solid chamber steel, 100%. An over pressure situation, in my experiences, almost always causes failure at the case head where it is unsupported.

I am still thinking that there are only a couple possible solutions, and since you say that sizing was not a problem, I'm going to have to go with a flaw in the sheet metal, or the drawing, that left some sort of weak spot in the shell.

Brass, as you all probably know, starts out as a heavy disk that is forced into dies with a mandrell, and the disc is forced into a cup shape and then stretched thinner and thinner. it's annealed a couple times as it work hardens. IIRC, there are over a \dozen stretching and pressure forming steps for a shell, then shaping,punching, and forming. That is a lot of working. In the initial draws, I am sure that at some point, a fold or weak spot could have occurred, and as more and more reshaping took place, that weak spot could be hidden. Then, given high pressure and stretching, it could have failed, as the cartridge forward of the case head expanded faster and farther than the case head did.

I can say one thing, I suspect that this failure happened real early in the igniftion. That is the only reason I can think of for all the sooty black burns. If the entire charge had ignited and reached peak pressure, ther should not ahve been so much loose carbon in the gasses. The bullet may not have even completely left the casing yet.
 
Have had several experiences w/ancient brass splitting. First noticed rem 7mm mag 20 something yrs old when I noticed a small groove appearing perpendicular to the mouth of the case where the crimp rolls into the channelure. Few yrs later the groove went all the way thru splitting the neck. As said seen several instances IIRC all were rem brass. Does it age harden? Can't say :confused: but based on the foregoing my take is some formulations may stress fatigue when under a certain amount of stress/tension. Even today, I make it a point to chk for groove starting to appear right at the roll of the crimp ~ and find some. Never had it happen w/my reloads but then again, I don't factory crimp them. I don't see it applying in your situation, just offering my personal observation/experience in response to the question re age hardening. I just can't imagine the case head having complex stresses that the neck/mouth does.
 
Just a note. Rings can appear at the base with new brass with chambers that are within spec. so it is always not indicative of excessive stretching of the case. Some rifles even new ones have loose chambers which will cause stretching of the case. I have a new 700 CDL SF in which this is the case and after the initial firing to fire form it, I only neck size to prevent excessive working. A body die can be used to bump the shoulder if necessary to make it chamber after a few firings.

As mentioned above, it is good practice to check fired cases headspace with a headspace gauge and/or case guages. FLS cases should be checked against the fired cases to make sure there is not excessive sizing. I have found that with Redding dies when set up properly will FLS within spec. Competition shell holder are very handy in obtaining proper headspace when FLS. I for one never use range brass for high powered rifles and always start with new brass. Neck thickness should also be checked to make sure it is within spec. Sinclair makes a micrometer gauge which is very accurate. Typically after 5 or 6 firings I dispose of the brass especially with higher velocity loads. Not worth the risk.
 
Was the brass cleaned in an acid solution? If so you should always "bake" it at 300º F for an hour afterwards.

Stress corrosion cracking is a phenomenon where a synergistic action of corrosion and tensile stress leads to brittle fracture of normally ductile materials at generally lower stress levels. During stress corrosion cracking, the material is relatively unattacked by the corrosive agent, but fine cracks form within it. This process has serious implications on the utility of the material because the applicable safe stress levels are drastically reduced in the corrosive medium. Season cracking and caustic embrittlement are two stress corrosion cracking processes which affected the serviceability of brass cartridge cases and riveted steel boilers respectively.
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