What causes head separation in bottleneck rifle cases

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And by the way, the industral useage term for the case sticking to the chamber is 'Stiction'.

"Stiction is the static friction that needs to be overcome to enable relative motion of stationary objects in contact."
A mash up of static & friction (or more properly, initial friction).

MAN! My autofill/auto correct HATES 'Stiction'! I thought I'd never get it to stop trying to correct it!
 
The 60kPSI does exist everywhere according to physics. The force (lbs.) get distributed according to surface area (sq. in.).

The 1/2" brass disk in the 3500 PSI tank needs to support ~690 lbs of force while at the same time the tank sides (assuming 1' diameter by 2' long) are subjected to over 260k pounds of total force spread evenly around the cylindrical sides. If the tank is larger, the total force on the sidewalls goes up accordingly.

It's similar with a brass case in a steel chamber. For a typical rifle cartridge, the total force on the case walls is about 10X the force on the case head (due to differences in surface area). If you assume the coefficient of friction between brass and steel is .3, the force holding the case walls in place against the chamber is still about 3X the force against the case head. So the case walls stay in place, and if the pressure/force is great enough, the case head moves back, stretching the case in the area forward of the case head that's not locked against the chamber wall.
 
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Again, BBarn, you 'ASSUME' the case 'Sticks' to the chamber wall...
I don't share that opinion since there are zero signs of that case being forced into the chamber wall under tremendous pressure.

Under your working theroy, then an overpressure great enough to make the case head 'Flow' wouldn't happen, since the side walls would be much more prone to flow, the case sides would be compressed to the point the case got MUCH longer and intruded into the freebore/chamber throat, which would be quite obvious.

Under your working theroy, the primer pocket wouldn't expand, the case walls would flow first, again forcing brass into freebore & possibly the throat since the primer pocket has much less surface area or volume than the powder chamber.

Like I said before, I'm not selling it as a home game, think what you want...
And like I said before, the physics don't line up with the Stiction prevailing dogma, just trying to reconcile the two...
 
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Case head stretching isn't assumed. It is evidenced by the thinning of the pressure ring. That proves the case was stuck and the sides held forward as the head backed up. Pressure is not selectively distributed in the case. The fluid nature of the gasses sees that it is distributed all over the chamber. The cartridge case is like a scuba tank with walls so thin it needs the help of the steel exoskeleton provided by the chamber to keep it intact. It doesn't move back until the bullet moves, and in the high-pressure cartridge with very rapid pressure rise, stiction is present before the bullet starts to move appreciably.

There is no 60,000 psi sheer force against the brass, as the head stretches back and contacts the chamber before the bullet gets's fully clear of the brass and before that much sheer can develop. The head is stretching well before 60,000 psi is reached. Again, this is a dynamic event where simple static force calculations fail because the modulus and yield strength of the material doesn't dominate until the inertia of the head is overcome and there has been time for everything to equilibrate, which never happens because the bullet is gone before it can.

There's a good example on Varmint Al's pages of bolt thrust calculations. If you just take the peak pressure and the head area and try to calculate from that, you wind up with about twice the actual bolt thrust the lugs experience. By the time the head makes contact with the bolt and settles against it, the pressure peak has passed so it never sees full thrust. Dynamics are a pain to take into consideration, but all-important to realistic modeling of what is actually happening.

More directly, look at Varmint Al's page here. Scroll down below the plots to the second set of case pictures under Polished and Lubricated case, and then to the one below it for a sandpaper finish on a chamber. Give the animations time to load and run. See how much pressure ring thinning the sandpaper chamber's case develops and how little the polished case above it develops. This is because there is lower stiction with the lower friction coefficients between the brass and the polished and lubed steel surface. This allows a greater overall length of brass to fail to stick fully to the wall where it is thicker and to stretch to let the head move back by the amount of excess headspace. Polishing a chamber is a good way to maximize case life if you are full-length resizing.
 
Jeep,

Your assumptions above about my understanding are mostly incorrect. There is ample evidence of what happens and why among several of the posts/posters/references in this thread.

I don't plan to say anymore about the subject.
 
I don't share that opinion since there are zero signs of that case being forced into the chamber wall under tremendous pressure.
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I think you are overlooking the obvious. The case is absolutely "stuck" to the chamber walls by pressure, that's what obturates (forms the gas seal) the chamber during firing.

Ever see a case rim torn through by the extractor, or the entire case head ripped off because a semi tried to open before the pressure dropped enough? The case is absolutely stuck to the chamber at that point.

BUT, when the pressure drops, the brass "springs back" slightly, and is no longer stuck (held by pressure) and can be extracted without issue.

When loads are too much pressure, the brass is hammered harder by the pressure, and doesn't always spring back enough to release from the chamber and that can cause a failure to extract.

If it wasn't stuck it would come right out, so if it doesn't then it must be stuck.

As to the flutes in an HK chamber, they didn't put them there to let water out. That may be an additional benefit, but its not their intended purpose. Their function is to increase the amount of adhesion of the case to the chamber at a given pressure. Allowing the use of a lighter locking mechanism than would otherwise be needed. The flutes give more surface area for the brass to grip, AND also allow gas to flow back into the chamber between the case and the chamber, breaking that grip at the proper time.b That's why they get so dirty.

again, the case is absolutely "formed" to the flutes, but then the combination of the brass springing back and powder gas prying it loose, allows extraction.
 
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Maybe the best way to look at this is as I have told others.

You can spend tens of thousand of dollar on an engineer who may or may not come up with the right answer and you want to correct the issue anyway.

Or you can just fix it with known techniques.

So, by empirical evidence by NOT doing a full case resize to the cam over point all the die mfgs call for (ie doing the so called impossible shoulder bump back) that delays the crack forming hugely (on my brass, I don't do Magnums)

I go with if it quacks like a duck, fly's like a duck, has webbed feet like a duck then the DNA will likely say its a duck.
 
Well this is going pretty much how I expected . Everyone cruising down stream while one keeps fighting the current to get up stream .

I’ll add another example JH that you say never happens that happened to me . That is the roughness of the chamber wall transferring/imprinting it’s pattern on to the case . I don’t remember which AR barrel but i bought a cheap one and after firing I can see the tool marks on my cases . Im on my phone right now and can’t upload the photo but Have a pic of the fired cases clearly showing the imprinted tool marks . I’ve since polished the chamber and no longer see the tool marks on the fired cases .
 
Case head stretching isn't assumed. It is evidenced by the thinning of the pressure ring. That proves the case was stuck and the sides held forward as the head backed up.
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Unclenick, 99% of the time I'm right there with you on things, but not this time...
What I see are results of firing. How the case got into that condition is where I differ with dogma.

Yes, the case stretches & thins, mostly just above (or in front of) the head/web.
The current dogma is the firing pin drives case forward,
Front of case bloats/sticks first,
The back of case moves rearward stretching the case.

I don't see it happening that way.

What I see is bullet movement pushing case backwards at the first couple hundred pounds of pressure, what ever it takes to dislodge the bullet from the case.
The pressure the primer produces can easily squib a bullet out of the case into the barrel...

When bullet dislodges, the case MUST move backwards.
The primer is indented, even if firing pin is fixed, the dent in the primer will seat right down around the extended firing pin, and the case hits the bolt face...

Now, anyone that's ever left powder, particularly rifle powder on a painted bench top, or on a piece of paper knows you have a stain.
The ONLY way you can have a stain is something running out of the powder... That means an non-compressible liquid.

The pressure starts in the back of the case with the primer, the bullet unseats overcoming any forward movement... The primer dimpled sits right back down over the firing pin, no matter if it's retractable or not.
The burn starts in earnest in the rear of the case and throws NON-BURNING powder forward against the shoulder & bullet which is now in the throat.
Bullet moves forward, case moves rearward with enough force to overcome firing pin (dented already), and the few pounds of ejector spring force, assuming there even is a spring loaded ejector...

The case is fully rearward pressure wave moving forward compressing powder that has SOME moisture in it (again, can't leak/stain or vapor off attacking plastic powder bins if it's not VOC),
That same moisture is why powder clumps when compressed.

That same moisture becomes a hydraulic hammer against the bullet & case shoulder.
At this point, the HOTTEST part of the case stretches, and the THINNEST part of the 'Hot' stretches the most.
That would be just above the head/web.
The thicker case head works as thermal mass, a heat sink, the case sides back where the powder is burning hottest is thinnest spot exposed to that heat, it's what stretches when the pressure expansion wave hammers the case neck (and back of the bullet sizing it in the rifling).

I could be wrong, but it fits the physics better than the shoulder/neck of the case (little surface area & extreme reverse angle for gripping anything) holding the case forward, even with gas jet venting forward, combined with the mass of the bullet exiting the case long before there is enough pressure to expand the case...
 
Look, MG,
1,500 years ago the 'Experts' absolutely KNEW that dirt & water combined made frogs.
The idea of dormant eggs never occurred to them.

Until magnification showed humans harmful bacteria, the 'Experts' absolutely KNEW it was evil spirits causing illness.

No matter how much math & models showed the earth rotated around the sun, the church/governments were still burning people at the stake as late as 500 years ago because they were 'Experts' and absolutely KNEW the Earth was center and the sun orbited it.

The 'Experts' absolutely KNEW the entire UNIVERSE was our galaxy.
Then someone built a telescope strong enough to see the other galaxies.

It's not up to me to decide what you 'Believe'. It doesn't effect me in the slightest.
A theroy that runs contrary to dogma always encounters violent opposition.
Either you have an open mind and will do the analysis yourself, or you will stick to dogma because thinking makes your brain hurt...

I've heard the same dogma repeated with slight changes for 40 years, it just took me about 35 years to gain enough first hand education to spot the holes in what's now dogma, so I don't 'Believe' it, rather electing to extrapolate a theroy that fits what I'm actually seeing...
Doesn't make my brain hurt to think it through!

I see results of stretched cases, I just don't happen to think the dogma currently 'Believed' fits the physics to reach those results, no matter how many times it's repeated, rehashed or recirculated here or there...
Repetition doesn't plug the holes in the theroy.
($30 off $3,000 worth of parts you can't use for anything still leaves you $2,970 in the hole, no matter how many times the manufacturer says it's exactly what you 'Need', but not what you ordered)

And again, I stress that if the front of the case locked down first, and the rear of the sides stretched allowing the head to NOT EVEN reach the bolt face (primer partly ejected),
Then how in the world does the back of the case flow first under overpressure conditions?

That would mean the head never reaches the bolt face AT ALL since the primer takes 10 pounds to CRUSH is protruding from the head, but the recoil/bolt face never produced 2 pounds to reinsert it into the primer pocket, or 10 pounds to crush it...

I get the entire cycle, and I've given you 100% of what you asked for, too long headspace or too short of case, but still fits the headspace well enough to both set the primer off AND a case that's grossly undersized so it can slop forward, but still big enough to lock to the neck/severe reverse sloped shoulder so the case can lock in front to rear...
A fixed firing pin that doesn't retract,
An in bolt ejector with 9,000 pound spring,
A primer that is both soft enough to deform under the firing pin strike, but hard enough to back out and NOT deform into a smeared pancake, strong enough to move a locked bolt rearward, but it still doesn't add up...
Anytime your theroy needs every part to go BOTH WAYS to work, it's highly probable it's not a correct theroy...

As to having an AR clone with a severely screwed chamber, it happens.
I said MY BUILDS don't leave the shop that way.
And,
You proved exactly what I stated, when you have a chamber so screwed it imprints the brass, it's time to see a gunsmith! Do not pass go, do not collect $200.

HK fluted chambers don't imprint brass with linear lines, and that's with higher pressure NATO ammunition and GD/ATK/Federal brass...
That striped brass once cleaned looks and specs out just like the rest of the milbrass I see...
I have to assume, since half the chamber is cut away in grooves, effectively DOUBLING the pressure on the lands, and still no 'Wavy' case sides from all that intense 'Lock Up' pressure you guys talk about, the case sides aren't NEARLY as weak as you all claim here, but in the annealing threads claimed it was suicide to allow annealing to creep past the lower shoulder bend...
Again, the 'Dogma' seems to need things both ways to work out the existing 'Theroy'.

YOU proved my point.
Are you aware the 'Import' barrels can be had for $12 USD when you buy a gross or more?
Under $20 when you buy a dozen or more.
I have no idea what they are made out of, but they look to be machined with a brick chip & hand drill so I won't use them...
I'd say as fast & uneven as the throat erodes and the rifling chips off or flattens out, I'd have to guess recycled pork & bean cans, but I have no way of knowing, which is the point and why I won't use them.

I'm going to bed now, been up since 1:30am and getting up at 2:00am.
You all recycle the dogma, or hash out something that actually fits the circumstances, makes no difference to me what you all settle in as individuals or as a group.
'Believe' what has been hashed over, or think it through for yourselves.
Good night.
 
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Good morning JH:)

1,500 years ago the 'Experts' absolutely KNEW that dirt & water combined made frogs.
Click to expand...

LMAO , yeah the earth was flat to I believe lol :D Not a lot of science and testing going on back then either . How ever we now have SAAMI , Hornady , the military all doing test on this stuff . It's not like all those organizations are just thinking this stuff up and writing "theory" papers .

I've not seen Slamfire around in awhile . I'd sure like his take on this .

A theroy that runs contrary to dogma always encounters violent opposition.
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Well that's a bit exaggerated there don't ya think . Is that what you think is going on here ? Theory is just that . Since others in the industry believe there test prove there theory . It's on you to prove your theory , not on us to believe it .

I enjoyed the debate in the other thread and enjoy this one as well . I hope you are not taking this to personally , that is not my intent but you are going against the tide . If that's your position then own it and don't complain when challenged . Making the argument that others in the past were wrong so that makes your theory possibly right is not a good argument IMO .

It does not help when you first claim that it was fact that primers can't stay backed out after firing . You have since softened your stance on that but you were quite sure of your self at first but you were wrong unless you believe I was lying when I posted my data on primers backing out . I know you were wrong at least one other time about something you first stated as fact . I don't remember off hand what that was but could find it if need be but there is your statement claiming there is not enough pressure pushing on the case walls to imprint chamber imperfections on to the case . I have pics showing that very thing happening . We are all wrong sometimes , it's the inability to except it that harms ones credibility . Maybe you should let me know if you still believe primers can't stay slightly backed out of the pocket after firing ?? If you still think they can't be backed out then maybe we are just going round and round and are debate will never be satisfactorily concluded for either of us ?
 
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Lots of characters and I’m tired but it looks like there is some difference of opinion to some degree.

As I said, not sure exactly where or how but I have another idea that might help answer some questions or raise others.

Take rimmed or belted bottle neck cases and test side by side with rimless or rebated ones. No matter how far you push the shoulder back on the first two there is only so far they can go into the chamber.

May not be much of an eye opener though as the extractor is going to have hold of the rim to some extent as well. A rimmed with a tiny o-ring would be held as firmly against the breech/bolt face as could be expected though.

It might also help to take everything one step at a time to see what happens.

Like take just a primed case and “fire” it. What is the condition of the primer at that point? If you take the same case and the next primer in the container and load a round and fire it, what are the differences and how does the exact loading effect the results?
 
Yes some do . But the HK rifles use a system where the bolt starts to move rearward while the pressure is still very high .That helps stretch the case . But that's a military rifle where # of reloads is not a consideration !
The flutes are there to help prevent the case head from being torn off ! [positive extraction ! ] The lines on the case help you get back your own cases ! The pistols are fun keep the RO to your left otherwise the ejected case will hit him in the head ! The case goes about 15' .

The comment about Glocks being hard to machine is due to the carbo-nitriding on the surface. That if further improved by a process that prevents rusting !
 
Here are those 223 cases with the chambers tooling marks imprinted on the case


t22PsT.jpg
 
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JeepHammer said:
Unclenick, 99% of the time I'm right there with you on things, but not this time...
What I see are results of firing. How the case got into that condition is where I differ with dogma.

Yes, the case stretches & thins, mostly just above (or in front of) the head/web.
The current dogma is the firing pin drives case forward,
Front of case bloats/sticks first,
The back of case moves rearward stretching the case.

I don't see it happening that way.

What I see is bullet movement pushing case backwards at the first couple hundred pounds of pressure, what ever it takes to dislodge the bullet from the case.
The pressure the primer produces can easily squib a bullet out of the case into the barrel...

When bullet dislodges, the case MUST move backwards.
The primer is indented, even if firing pin is fixed, the dent in the primer will seat right down around the extended firing pin, and the case hits the bolt face...

Now, anyone that's ever left powder, particularly rifle powder on a painted bench top, or on a piece of paper knows you have a stain.
The ONLY way you can have a stain is something running out of the powder... That means an non-compressible liquid.

The pressure starts in the back of the case with the primer, the bullet unseats overcoming any forward movement... The primer dimpled sits right back down over the firing pin, no matter if it's retractable or not.
The burn starts in earnest in the rear of the case and throws NON-BURNING powder forward against the shoulder & bullet which is now in the throat.
Bullet moves forward, case moves rearward with enough force to overcome firing pin (dented already), and the few pounds of ejector spring force, assuming there even is a spring loaded ejector...

The case is fully rearward pressure wave moving forward compressing powder that has SOME moisture in it (again, can't leak/stain or vapor off attacking plastic powder bins if it's not VOC),
That same moisture is why powder clumps when compressed.

That same moisture becomes a hydraulic hammer against the bullet & case shoulder.
At this point, the HOTTEST part of the case stretches, and the THINNEST part of the 'Hot' stretches the most.
That would be just above the head/web.
The thicker case head works as thermal mass, a heat sink, the case sides back where the powder is burning hottest is thinnest spot exposed to that heat, it's what stretches when the pressure expansion wave hammers the case neck (and back of the bullet sizing it in the rifling).

I could be wrong, but it fits the physics better than the shoulder/neck of the case (little surface area & extreme reverse angle for gripping anything) holding the case forward, even with gas jet venting forward, combined with the mass of the bullet exiting the case long before there is enough pressure to expand the case...
Click to expand...

You've made many 'factual' statements. Can you please cite the references that support these statements so we can read up on the subject? Thanks in advance.
 
 
HK fluted chambers don't imprint brass with linear lines . . .
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They can and HK isn’t the only one CETME, some scheumann barrels, and a number of other older firearms that I can think of.
 
The person making the claim has the burden to prove his assertion. In this case that "modern science" has it wrong and that every known recognized expert in the field doesn't really understand what's happening.

If I'm understanding Jeep's position correctly, a simple experiment should prove the point.

Size a bunch of relatively identical cases so that they are, say 0.01 shorter than the chamber. Pick a load to use for all sample cartridges that is low enough to be used with bullets jammed in the rifling but high enough to be well above 30k PSI WITHOUT the bullet jammed in the rifling.

Make the same number of rounds with and without the bullet jammed in the rifling. Mark the cases so they can be differentiated, as they will all have to be fired repeatedly under the same conditions.

If Jeep is right, all the cases will exhibit head separation after a few firings, since he believes the cases are stretching forward. If he is wrong, only those whose bullets were not jammed in the rifling will separate, since the ones with the bullet jammed in the rifling will not be able to stretch backward.
 
Size a bunch of relatively identical cases so that they are, say 0.01 shorter than the chamber.
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"say 0.01 shorter than the chamber"? I would say .001" shorter than the chamber from the shoulder of the chamber/datum to the bolt face; meaning the case would be sized .001" shorter than a go-gage length chamber or .004" longer from the shoulder to the case head than a minimum, length full length sized case. IF THE CHAMBER IS THE PERFECT CHAMBER.

One more time: I have a chamber that lacks .011 being the perfect chamber. If I fired full length sized/minimum length chases in that chamber I would have .016" clearance; the .011" makes the chamber .002" longer than a field reject length chamber.

When I fire cases in that chamber I have .002" clearance; stretch of the case has never locked me up or has it driven me to the curb, it is impossible for me to stretch cases with that rifle, I have at least 6 of them.

F. Guffey
 
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