Case head separation

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Before today, I had loaded tens of thousands of rounds without this happening.

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It didn't completely separate. The chamber fortunately isn't scored, and obviously I am fine.

But I am wondering what happened. This was 2x fired lake city, shooting a 175 grain smk with 41 gr IMR 4064 at about 2400 fps out of my AR 10.

I set the shoulder back 0.004 in all my semi automatic rifles.
I checked other brass from the batch and even cut a couple with my Dremel tool to look for thinner spots above the web and found none.... Nothing to indicate this was about to happen. I used my dental scrapping tool an several others to feel for a groove in some I have yet to load the 3rd time and some I already fired.

I guess what I am wondering is: Does this just happen sometimes of you shoot often enough? Or am I missing something?

I am very cognizant of casehead separation since I load for the .300wm a lot, but after thousands of rounds it hasn't yet happened in that chambering....Or any other gun I load for until today.
 
The only thing I know of that will do that is excessive head space. Used to see in in belted cartridge's. Because they head spaced on the belt, many chamber's were sloppy and the case constantly moving forward when fired, pulled on the case just in front of the head, belt. In the belted cartridge you see it develop as a ring all the way around the case at the head. You probably won't notice in a rimless case because it just doesn't happen much, better cut chamber's. I think you said your were using them in an auto? By partial sizing you can move the shoulder forward a bit and stop all the stretch. Probably be a good idea first to take it to a gun smith and check the head space. The gunsmith could probably fix it by shortening the chamber.

Keep in mind that a ring around the case head like that is caused by the case stretching to much. You can take unfired case's and shoot them in there and no problem. But, with an unfired case the problem doesn't do away, it simply hide's as it's gonn take two to four firing's to get to that point. Look at your other case's in the same spot and look for a ring all the way around the head. They will be the one's that are fixing to have the same problem.
 
Yes ! You should be sizing to a particular chamber , NOT to standard dimensions !
Much of that problem started with the 7mm Rem Mag !
 
In response to the posts, I can tell you that it wasn't excessive headspace. I size each piece of brass 0.004" back. Before firing using my headspace gauge the brass from head to Datum is 1.5905"....Fired case is 1.5945". So relative growth of 0.004".

Also, I have some federal brass I am on the 8th reload with and some FC 08 that is on its 6th load....So not headspace and I do obviously size to this chamber.

Keep the diagnosis going though, im not trying to be rude with my responses, just addressing the comments to help clarify.

Could I have over annealed?....I mean I use Tempilaq down the side (450) to make sure that I don't anneal the head. But that could explain it ???
 
I highly doubt that your anealing (especially using Tempilaq) had anything to do w/ it.
Call it an anomaly and continue to inspect cases with a dental pick as you're doing now.
(Did that case pass the pick test?)


As to using a fired case to establish your max case dimension, I suggest a change.
Find a case that when gradually sized increases in length enough to stop bolt closure.
Graaaadualy increase sizing/measuring until the bolt juuuust closes w/o feel.
That's your new baseline.
 
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Cases, fired or not, are never a reliable substitute for proper gauges.

That being said, one thing that can cause head separation in a semiauto rifle is the breech opening too soon. I can't determine if that is the case here or even what might cause that condition without an examination of the rifle and ammunition but it is one possibility.

Jim
 
History of the brass? Bought as once fired?

Factory ammo (brass) can be damaged on the very first firing, if there is excessive chamber headspace.

And/or there is extra head clearance (cartridge headspace).

Brass should not be swapped between different firearms. The shoulder set back may be different for each rifle.
 
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I determine the length of the chamber from the shoulder to the bolt face and then I measure the length of the case from the shoulder to the case head; the difference in length indicated the amount of case travel before firing. I am the fan of cutting down on al that travel. If the manufacturer does not sell cases that are too long for my chamber I form them or I purchases cases that have been fired in trash old chambers.

F. Guffey
 
The brass was purchased as once fired from sportsman's guide. I suppose some of it could have been fired from an unsupported machine gun chamber. It came sized and capped.

It isn't a headspace issue.. if it was, im sure it would have showed up somewhere in the first 2500 rounds I have loaded and reloaded in this rifle using different brands of brass, some of which is on its 8th load.

Also, I'm hip to all the obvious stuff like this:
Brass should not be swapped between different firearms. The shoulder set back may be different for each rifle
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It is my first ever casehead separation,...Not my first handload
 
That being said, one thing that can cause head separation in a semiauto rifle is the breech opening too soon. I can't determine if that is the case here or even what might cause that condition without an examination of the rifle and ammunition but it is one possibility.
Click to expand...

That is where I am leaning as well.

Could your rifle be over-gassed? That would make the bolt unlock sooner would it not? Just an idea....
 
Could your rifle be over-gassed? That would make the bolt unlock sooner would it not? Just an idea....
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Good question? It is a Ruger SR 762... Adjustable gas piston system. I am running on "2" but could go down to "1"..

I have always ran it on "2" and it never happened before, but that doesn't mean it wasn't the cause this time.

I suppose I'll run it on 1 for a while and as long as it cycles and extracts there is no upside to more gas
 
Maybe post up in the semi-auto forum and see what guys think? And yeah, I wouldn't run more gas than you need. That's just costing you velocity.
 
1 brass, 1 defect. Move on. Not a problem.
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I think this is probably the answer....But there are a few folks on here who have some good suggestions that I may not have thought about..... Adjusting the gas is a good suggestion, especially since it is easy to do on my gun.
 
When you buy "once fired" brass,its range pickup brass.90+ % might be once fired,but its not certified aircraft material.There is no "once fired" traceability.
The guy who left it may have loaded it eight times,and abandoned it.
If you have unprocessed once fired left,pull a sample of 100 or 200 rds.Paperclip (probe) test all of them. If you find a stretch ring on one piece of brass that has not been through your rifle or loading process,you have your answer.
 
Trimming to Minimum length than resizing with a small base die can enhance such a case separation "I suppose."

Than again I won't reload second hand LC brass. Nope!! never. LC gets culled to the junk box on my reloading bench.
 
I like the idea that it's a random fluke too. (But just cause I like something doesn't mean it's true.)

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?

Sounds like you're going to try out some stuff. When you do please come back and tell us the results. And thanks for including the pictures, and the bigger picture.
 
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