What is the cause of head separation in cases?

Thank you for your input.

Buliwyf

chamber/headspace too long or the case is unsupported in someway. Cases stretch and separate if you size them down too much, pushing the shoulder back sometimes. I hope I explained that correctly. The case is over elongated for several possible reasons when fired. The round is fired and the brass flows forward causing the area in front of the thick brass base/casehead to pull apart. Anytime I start seeing a bright ring on the case head, I bend a paper clip and see if I can feel an internal crack. It is then time for new brass and a die adjustment. I split a bunch of 17Ahs from using too light a load to fireform a while back.

I'll try a little differently....but blueprinted is dead on...

If the chamber has a lot of headspace.....the cartridge is pushed foreward to the shoulder by the firing pin and then detonated.

The pressure of the gas causes the case to expand the cartridge walls to the chamber and is held tightly but then the case head is forced back against the bolt face a bit and the brass is forced to stretch in the only place it can.....the area just ahead of the web.

Full length resizing then sets the shoulder back again and the next firing again thins the brass immediately ahead of the web.

In some cases the headspace is so severe the case can break in two firings!!!!

If one is chambering a barrel it is advisable to chamber as close to the go-gage as possible and possibly dead on to the gage.

This results in longer brass life.

This is also why one can solve headspace problems simply by not full length resizing.....merely set the die back from the shell holder 1/4 turn so you don't push the shoulder back.....ensuing firings then will not push the case foreward in the chamber and thin the web.

May I also add that case "stretching" does occur during each firing, coupled with repeated firing and resizing, will naturally cause the case to wear thin above the web.

5 reloadings for a rifle case is about average. There are various factors that can affect case life... mild loads, better than SAMII specs on headspacing, better quality brass,.... etc.

The point is this, If the ring appears on just one case in a batch, I throw the whole batch out and replace them with fresh brass. I ususally get 5 loadings out of a batch when FL resizing... and 6-8 loadings when I use neck sizing. Eventually, if you shoot it, brass will wear out.

Personally, I don't like a case that drags on the bolt face as I close the bolt, so will FL resize to the point where it will just chamber without the drag. I get better accuracy, no feeding/extraction problems, and I am content with 5 reloadings per case.

Others on this site have said they like to feel a little drag on the bolt. To each their own.

General Advice on Small Base dies and Wilson case gages.

Vapodog and Blueprinted are spot on with the description of case head separation. Let me add more material, maybe of some help, maybe not.

Gas guns, particularly the M14/M1 Garand and the FN/FAL are hard on brass. All gas semiautomatic gun mechanisms unlock when there is still residual breech pressure. The pressure is typically under 650 psi, (exact value depends on pressure curve, but it is never enough to rupture the case) and that pressure increases the available time there is energy to operate the mechanism. That residual pressure also causes a lot of case stretching. Cases are still sticking to the chamber walls when the rifle mechanism unlocks. So if you reload cases fired in the afore mentioned mechanisms it is only a matter of time till you start experiencing case head separations. Depending on the rifle, sometimes you will get only five reloads on a case before incipient case head separation.

If you size for a bolt gun, are using standard rimless cases, and you are only setting the shoulder of your case maybe .003†or so, you can reload that case indefinitely without the worry of a case head separation.

Now to get around to what I think will be value added for you, assuming that you are a new reloader. And that is advice on setting up your sizing dies so you do not oversize cases as mentioned by earlier posters.

The set up instructions given with sizing dies assume a lot of things. And seldom following the instructions do you ever get the brass sized to the correct length. If possible you would like to set back the case shoulder about .003†from the fully expanded condition it comes out of the rifle. You never want to size it more than .006†as you are likely to get a case head separation on the next firing. Sometimes following the instructions that come with the sizing die you will not be able to even set the shoulder back enough to avoid a crush fit in the rifle chamber. In a few instances I have had to grind material off the bottom of a sizing die to get it to set the case shoulder back enough. Just take the instructions that the factory sends with their dies, and toss out the part that tells you to size to the shellholder. Or shellholder plus a ¼ turn. You will find that such guidance is inaccurate at best, rubbish on the average.

To properly size cases to a correct length you will need a piece of equipment that has not been mentioned: case gages. I really like the Wilson type case gage. You size your round and drop it in the gage. This gage measures the distance between shoulder and base. It is a "go" and "no Go" gage. And it is a true measurement, as I have dropped my chamber headspace gages in my wilson gages and found perfect agreement between them. You want to size your case between “go†and “no goâ€, and for my rifles, I size most everything to gage minimum.

If you want to try an experiment, size the case following the factory sizing die instructions. Then measure the sized case length with your case gage. If the case is between the “go†and “no go†of the gage, go buy a lottery ticket. Because it is your lucky day and you are going to win the lottery. What you will probably see is a case that is over length. On a few occasions you will see an underlength case.

This web site is really useful for showing how to use case gages. I recommend looking at the pictures, and it explains the special case gages needed for the belted cartridges.

http://www.realguns.com/Commentary/comar46.htm

The midsection of the Wilson gage is cut big. It only measures headspace. What the Wilson type gage and the other functionally equivalent gages do not measure is "fatness". This is an important measurement for gas guns and should be controlled. You do not want any resistance to bolt closure due to overlong cases or over fat cases. It is a safety consideration for gas rifles with free floating firing pins, it is a reliability consideration for the other few actions. The answer is not to reduce the case length excessively, for then you risk headspace separation. The answer is to use small base dies in conjunction with case gages.

I have a 300 Win Mag. And like others have said to much headspace and full lenght sizing. But in my case what has accerlated my case head seperation was hot loads. I really wish I could get some digital pictures on here. I have some great examples of the progressive stages of case head seperation. I have learned a lot about the topic...the hard way. First time I heard a pop in my Ruger #1 300Win, went to eject and the only thing that came out was the head. The next and last time was in my Savage M110 30-06. So its not just a belted case thing. Now even my 300Win is headspaced off the shoulder, partial necked sized, and once I notice the very fine lightly colored line around the head area, the brass gets tossed.

Thank you for your input.

If the head is the "thickest" part of the case why does it separate at this point and not in the neck or body?

quote:

Originally posted by Buliwyf:
Thank you for your input.

If the head is the "thickest" part of the case why does it separate at this point and not in the neck or body?

I think my description explains this...read it again and let me know if you're still in question on this.

The body wall is gripping the chamber wall, the head being thicker (and often not fully supported) dosn't expand as much and is free to move back aganst the bolt face. Where the stretching occurs is at the junction of the thicker head material and the thinner wall material.
Cutting a new and multipal sized/fired in half, lengthwise, will allow you to see exactly what and where this is happening.

Thanks vapodog. I went back and read your and everbody's again and along with Tailgunner's post the light went on. This is one of those subjects that must be simple once you understand it.

I'm trying to take my handloading to a higher level. I've been reading the die instructions and following those even tho I didn't completely understand "why".

I haven't thought in terms of the bolt lugs moving within tolerance allowing back thrust to stretch the case backwards - I thought the case stretched forward. So, the "thinner" parts of the case grip before the "thicker" parts can grip the chamber walls and the case moves "back" toward the shooter not "forward" thereby stretching the head area. Ok.

Is this the same whether belted case or not?

Buliwyf,
for less than the cost of a set of dies, buy a head space gauge for each calibre you reload. Just drop your resized round in and instantly you will know if you are within specs. Most head space gauges will give you a reading on both head space and case length. The peace of mind is worth it.

Buliwyf,
Sent you a private message.. kinda long

quote:

Is this the same whether belted case or not?

A belted bottleneck case has two places that it can headspace. Unfortunately, manufacturers take advantage of this by making chambers for belted cases outrageously large and depend on the belt to take care of headspace. However, there is no reason that you cannot headspace your belted/bottleneck case on the shoulder on subsequent firings.

The best practice has been described previously and it boils down to this: Screw your full length sizing die into the press only as far as necessary to allow the reloaded cartridge to chamber without excessive force on the bolt. This way you will be headspacing on the shoulder, whether rimmed, rimless, or belted, and your headspace will be minimal for your particular rifle. Resized this way and loaded to moderate pressure, rifle brass will last for many firings, ie. necks will split or some other problem occur before you'll run into an incipient head separation.

quote:

I thought the case stretched forward. So, the "thinner" parts of the case grip before the "thicker" parts can grip the chamber walls and the case moves "back" toward the shooter not "forward" thereby stretching the head area. Ok.

Is this the same whether belted case or not?

yes...now you got it.....and Stonecreek did a great job of answering the last question.

Thanks for the comments.

I'll guess the chambers are "larger" cut on the belted bottleneck cases because of the variances of belt width and/or belt thickness.

It is the primer that pushes the case forward.
Pressure hold the case forward until some medium pressure is reached (40 kpsi or so in a dry chamber). Once this pressure is exceded the case comes back forcing the primer back into the case.. The stretch occurs wherethe case begins to thicken.
This is why: Primers protrude from cases fired at low pressure with headspace, Primers look "riveted" in cases with high pressure. Low pressure loads will not fill out to full length.
If the case is oiled, it will fill out evenly and not stretch at the thin spot.
Good luck!

Hawkins,
please explain the "case is oiled" part of your posting. Surely you do not mean putting a case with any kind of lube in your rifle and firing it off? Would this not unneccesarily increase bolt face thrust?
Tks,
J

quote:

Would this not unneccesarily increase bolt face thrust?

I don't want to open an entirely new thread here, but the idea that a lubricated case increases bolt thrust is a common one, however it doesn't stand up to scrutiny.

Think about it this way: If bolt thrust is decreased by friction between the case and chamber walls, then the case walls are resisting stretching under some 60,000 psi to keep the case head from pushing against the bolt. Does this make sense?

Viewed another way, if you could remove the bolt completely and set off the primer with a punch inserted from the rear of the action, then you are saying that an "oiled" case would come shooting out of the chamber backwards, but that a dry case would grip the chamber and fire normally. I doubt this. Instead, the dry case would grip the chamber and the 60,000 psi would rip the case head off and IT would come flying backwards out of the chamber. Either way, the bolt face must contain the 60,000 psi.

I do suppose that "bolt thrust" could theoretically be reduced in a dry chamber by the amount of stretch resistance of the case, but that would appear to be de minimus.

quote:

Originally posted by Stonecreek:
I don't want to open an entirely new thread here, but the idea that a lubricated case increases bolt thrust is a common one, however it doesn't stand up to scrutiny.

I do suppose that "bolt thrust" could theoretically be reduced in a dry chamber by the amount of stretch resistance of the case, but that would appear to be de minimus.

Exactly.....I agree completely.

When fireforming cases for the first time in a bolt gun I make sure the chamber is very clean and rub a slight (and I mean slight) film of gun oil over the front 2/3 of the case. I rarely see protruding primers with this technique. I have used as many as 4 techinques at the same time to prevent case stretching at fire forming.

1. Tight shoulder fit against the chamber
2. Bullet again lands
3. Case mouth against a square ended chamber shoulder such as a military Mauser
(don't waste time with #3 if you can help it)
4. Lightly oiled cases

The Japanese 6.5MM light machine gun used in WWII used a cartridge oiler to insure it functioned well.

Here is more than you would ever want to know about the subject of back thrust, chamber finish and friction.

Effects of back thrust, friction and finish

Well to take this thread down a lubricated case rathole, a lubricated case is in fact better for function. A designer does not want breech friction. The load that a 30-06 cartridge gives on a bolt face is about 4000 pounds. There are a lot of things that are more heavily loaded, wheel bearings for one.

As for a frictionless case, well if you could get it, you could have a lighter thinner extractor, you would not need as much gas to operate the mechanism, which would result in lighter operating rod, springs, etc. Unfortunately cases do stick and the designer has to build a heavier weapon because of it.

The weakest part of any cartridge weapon is the brass case. Brass stretches and ruptures a lot sooner than even the mildest carbon steel. Reduced to its simplest form, actions are designed to keep that cartridge from rupturing.And if you go to the web page referenced by ireload2, you will find that lubricating the case actually reduces case head stretch, thus reducing the chance the case will rupture. Therefore improving the safety of the system.

Assuming that the cartridge pressure does not exceed max. An overmax load is not a good thing, an overmax load with a lubricated case is even worse.

As I mentioned a case stays forward until some pressure is reached. Once the case moves back it has the same force on the breech oiled or not. With a dry chamber you can (theoretically) fire a cartridge without a breech. Ackley fired a 30/30 with out the lock. Many of the olt timer 22 single shots didn't have breech blocks, just a heavy hammer.
Good luck1

quote:

Originally posted by hawkins:
With a dry chamber you can (theoretically) fire a cartridge without a breech. Many of the olt timer 22 single shots didn't have breech blocks, just a heavy hammer.
Good luck1

Hawkins...let me try to understand this.....as I could be wrong on this...ok?

If I understand it you're saying that if I took the bolt out of my M-70 30-06 and totally ground off the two front locking lugs and disabled the bolt handle from engaging in the action.....assuming I had a bone dry cartridge and chamber and the chamber has not been polished after reaming, that the firing of the cartridge would not cause the bolt to fly away from the action?

It's been posted before that the brass in the 30-30 is heavy enough to not stretch at normal 30-30 operating pressures. In the case of the 22LR's, the hammer has enough inertia to prevent the case from moving backwards, so neither is realy a valid test cartridge.

Over on 24hour, their was a interesting test run on the bolt thrust of std vs improved chambers http://www.24hourcampfire.com/ubbthreads/showflat.php?C...&an=0&page=0#1135303 The results are something that I found to be very suprising, IE: that the "improved design" has LESS chamber wall grip than the "standard" design does.

Vapodog; When did I say that??
What I said is a case will stay forward until some MODERATE pressure is reached.
There are many examples of this, read what I said about protruding primers and headspace.
there is no other explaination why "headspace' will; 1. Cause protruding primers, 2. Cause riveted primers.
Take Care!

quote:

Originally posted by hawkins:
Vapodog; When did I say that??
What I said is a case will stay forward until some MODERATE pressure is reached.
There are many examples of this, read what I said about protruding primers and headspace.
there is no other explaination why "headspace' will; 1. Cause protruding primers, 2. Cause riveted primers.
Take Care!

OK...I was sure I misunderstood....

Valuable discussion, everyone!

Think about what your sizing dies are doing.

Typical head separation (270)

http://www.varmintal.com/a243z.htm Put to much power in a case, or fire a max. loaded case more then 3 times, you may get a head separation. More likely with an unsupported case thats been FLRS. But neck sized only brass will do it also, because the bolt face does not fully come in contact with the barrel in most all Rifles.

quote:

Originally posted by Buliwyf:
What is the cause of head separation in cases?...

Excess Headspace - it's really just that simple.

Good hunting and clean 1-shot kills.