Case head separation?

[engineer40]

A first for me... I had a case come out of the chamber in 2 pieces the other day, separated at the case head.

The case was on it's 4th firing.

Since I was loading right towards the top of the load data, I had been checking for pressure signs every firing. I saw none. Primers always looked good. Nothing funny looking on the case head. Cases always extracted easily. Primer pockets weren't loose at all.

I shot 20 rounds that day loaded identical. Only had that 1 case come apart.

This is a newer rifle for me. I'm trying to think through what could have caused this if I wasn't seeing pressure signs. Is there a chance that my chamber is too large or the sizing die is too small? It is a factory barrel. When I measure fired cases just above where the 1 case had the head separation, they measure at 0.479. When I measure a case that I've already sized they measure 0.473. Is 0.006 too much to squeeze brass back down?

This is a straight walled magnum cartridge. There is no shoulder to measure. But when I full length size standard rifle cases, I usually only bump the shoulder back around 0.002 to 0.003.

Any of you guys experience case head separation when you weren't seeing pressure signs? Obviously this makes me a little nervous to reload ANY of the cases again. Thanks!

 

[tbrice23]

I would not fire any more until you bisect a few cases for inspection.

You should get a Hornady Headspace Bushing. I have to believe maybe you could be FL sizing your cases too far. ???? Maybe.
I cut a couple of cases apart once in a while to inspect for problems.

 

[Garycrow]

This is a straight walled magnum cartridge.

What cartridge?

 

[cape cove]

I have only experienced case head seperation when I pushed my case shoulders to far back due to a mis-adjusted die. I believe even excissive pressure will not seperate a case head unless the shoulder is pushed too far back. I have no experience with straight walled cases.I believe you would have to adjust your die to headspace on the case mouth if that is possible with a belted straight walled case. What cartridge are you loading for.

 

[WildRose]

Many moons ago Jimmy and I had to make a flying trip up to the ranch because we were in a terrible cold wave blasting in straight from the arctic.

We spent roughly 10-12hrs a day cutting ice and pulling it out in huge sabs with a tractor so the cows could drink at least twice a day.

Six days later when we get home it dawns on us that we left the tumble on full of .220 Swift and 7RM cases.

When we started resizing them we learned quickly that the excess tumbling had actually ground away so much material they were just trash. That's the only time I've run into such a problem. Some cracked at the shoulder and neck and some around the case head of the 7RM's.

Thin, weak brass will do that too you.

 

[243winxb]

460 S&W Magnum - The sizing die is working the brass a lot. But to get the correct neck tension on the bullets, it has to. Neck tension is important for a revolver, not as much for a TC single shot.

Try "neck sizing" RCBS has said to size the brass just below where the base of the bullet ends.

Trial and error, making adjustments , size more if needed for brass to fit the chamber.

Size just enough of the brass so that if will fit the chamber.

 

[243winxb]

The die has to size extra small in diameter to allow for thin walled brass differences, between brands.

 

[engineer40]

Wow, that's why I love this forum. Thanks everyone for the fast responses!


You're correct, it is a 460S&W in a TC Encore rifle. And it is my first time working with a straight walled cartridge. (I do have the Hornady Headspace gauge for cartridges with shoulders to measure).

I just got my reloading dies for my 450 Bushmaster which is also straight walled. So I really want to make sure I am doing everything correctly.

That is interesting idea of only "neck" sizing a straight walled case. It will take some experimenting! I never thought to even try that.

I don't have a problem sawing a couple of these cases in half to inspect them. I do agree, that is a good next step! Thanks!


I had a feeling I was working the brass too much. I also load for 303 British and I'm super careful to not overwork the cases because those rifles are notorious for loose chambers. I have never had a case head separation on my 303 Brit, but that's because I read about the problem before I started loading for it.

 

[243winxb]

The other option is, reduce the powder charge , if you continue to have separations.

At maximun working pressures, 65,000 PSI , Case life may be short.

modulus of elasticity- Cartridge Brass-
Material is 70 copper/30 zinc with trace amounts of lead & iron , called C26000. Material starts to yield at 15,000 PSI when soft (annealed), and 63,000 PSI when hard.
Material yields, but continues to get stronger up to 47,000 PSI when soft, and 76,000 PSI
when work hardened. Modulus of Elasticity is 16,000,000 PSI. This means to pull a 1.000 inch long strip to 1.001 inch long induces a 16,000 PSI stress.
So if you pull a 1.000 inch strip to 1.005 inch long, you get about 76,000 PSI, which is the max obtainable.

From Olin Brass.

 

[bigedp51]

A fired case can stretch in two directions.

1. If the case has excessive head clearance meaning excessive shoulder bump. This also applies to the first firing and its possible for a belted case at maximum headspace and with a thin belt to have .015 head clearance.

2. The case can stretch outward to meet the chamber walls and add more to the case stretching.

I collected British Enfield rifles and at maximum military headspace of .074 and a rim thickness of .058 you would have .016 head clearance.

Below is what happens on the first firing with excessive head clearance in a .303 Enfield rifle.

Below is a factory loaded Winchester .303 sectioned case that stretched .009 on its first firing. The headspace was under SAAMI limits at just below .067 but it still had .009 head clearance.

Moral of story, don't let the case stretch on its first firing and keep shoulder bump at the minimum.

Second moral of story, don't shoot thin SAAMI Winchester brass with thin rims in a military British Enfield .303 rifle with a long fat military chamber..

Third moral of story, rimmed cases and belted case are a design dating back when manufacturing tolerances were very crude. The British came out with the first belted case and they used cordite powder that looked like spaghetti and cut to case shoulder length. The cordite powder was placed in the case "before" the shoulder and neck were formed. And on rimmed and belted cases the location of the shoulder was not critical.

Below on the left is a brand new unfired Winchester case, in the middle is a reloaded case fired the second time. And on the right the same case reloaded and fired a third time and just ready to seperate.

Bottom line I'm guessing your belted cases stretched the most on their first firing and just kept stretching. My RCBS case mastering gauge pictured above is a great tool for measuring case wall thickness. Its a fancy $100.00 bent paper clip thats measures in thousandths.

I'm also guessing you cases might be thin just above the belt and possibly at minimum allowable case diameter. Meaning that brand of case is not user friendly in your chamber. If you have any new unfired cases check the case diameter just above the belt where the case seperated. And again after being fired to see how much the case expanded and again after full length resizing. You might also have a fat chamber and a skinny die and over working the brass.

Major Edit

Now after all this slow typing with two dyslexic typing fingers and posting all my fantastic photos I find out your shooting a non belted 460S&W pistol cartridge. So now I will give my final guess.

Your from Texas and you used too much Kingsford lighter fluid and overloaded your oversized handgun.

Really this isn't really my fault, I need new bifocals and find a braille reloading forum to hang out in.

 

[engineer40]

The other option is, reduce the powder charge , if you continue to have separations.

At maximun working pressures, 65,000 PSI , Case life may be short.


From Olin Brass.

That's really good info. Thanks for posting!

Even though the cartridge is rated up to 65,000psi, the max loadings in my books only go up to mid 40K's to mid 50K's PSI (depending on powder I've used; H110, IMR4227, and Lil Gun).

One other thought I had is that I might be crimping the bullets too tight. Most of the powders I've used, people say you need a tight crimp for reliable burn. But possibly I'm crimping too tight and creating excessive pressure? I'm using a Lee Factory Crimp die.

 

[engineer40]

A fired case can stretch in two directions.

1. If the case has excessive head clearance meaning excessive shoulder bump. This also applies to the first firing and its possible for a belted case at maximum headspace and with a thin belt to have .015 head clearance.

2. The case can stretch outward to meet the chamber walls and add more to the case stretching.

I collected British Enfield rifles and at maximum military headspace of .074 and a rim thickness of .058 you would have .016 head clearance.

Below is what happens on the first firing with excessive head clearance in a .303 Enfield rifle.


Below is a factory loaded Winchester .303 sectioned case that stretched .009 on its first firing. The headspace was under SAAMI limits at just below .067 but it still had .009 head clearance.


Moral of story, don't let the case stretch on its first firing and keep shoulder bump at the minimum.

Second moral of story, don't shoot thin SAAMI Winchester brass with thin rims in a military British Enfield .303 rifle with a long fat military chamber..

Third moral of story, rimmed cases and belted case are a design dating back when manufacturing tolerances were very crude. The British came out with the first belted case and they used cordite powder that looked like spaghetti and cut to case shoulder length. The cordite powder was placed in the case "before" the shoulder and neck were formed. And on rimmed and belted cases the location of the shoulder was not critical.

Below on the left is a brand new unfired Winchester case, in the middle is a reloaded case fired the second time. And on the right the same case reloaded and fired a third time and just ready to seperate.


Bottom line I'm guessing your belted cases stretched the most on their first firing and just kept stretching. My RCBS case mastering gauge pictured above is a great tool for measuring case wall thickness. Its a fancy $100.00 bent paper clip thats measures in thousandths.

I'm also guessing you cases might be thin just above the belt and possibly at minimum allowable case diameter. Meaning that brand of case is not user friendly in your chamber. If you have any new unfired cases check the case diameter just above the belt where the case seperated. And again after being fired to see how much the case expanded and again after full length resizing. You might also have a fat chamber and a skinny die and over working the brass.

Major Edit

Now after all this slow typing with two dyslexic typing fingers and posting all my fantastic photos I find out your shooting a non belted 460S&W pistol cartridge. So now I will give my final guess.

Your from Texas and you used too much Kingsford lighter fluid and overloaded your oversized handgun.


Really this isn't really my fault, I need new bifocals and find a braille reloading forum to hang out in.

Thanks for taking the time to type all of that up! It actually does help. I was new to TC rifles. When I was researching them I remember reading that if you are having accuracy issues, TC single shot rifles are known to sometimes have headspace issues because you can change barrels. So it seems likely there is a chance that my cases are stretching upon the first firing, not necessarily from my reloading. Thank you!


I think my first step will be to saw/dremel a couple cases in half and look at how thin the rest may be. Then I will try to load some and experiment with how little I can size the case and still get it to fit in the chamber.

 

[bigngreen]

On straight wall cases it's imperative to have cases clean and everything dry, the drag of the powder will actually try to pull the case down the bore and if you have no traction on the case wall holding the case in place you can have issue. Your no having the same issues you would with a bottle neck case, whole different ball of wax!

 

[243winxb]

I have bigedp51 on my ignore list. Theres a reason for that. To much BS.

But yet, someone quotes it, making me see it.