ANSI Y 1415M and 30/06 dwg.

[joeb33050]

We have a drawing of the 30/06 cartridge and chamber.
There's interference between the largest cartridge and the smallest chamber, and the smallest cartridge and largest chamber leafe .013" headspace.
I know just enough to know that this isn't what the drawing means.
Is there anyone here familiar with the ANSI spec/modern dimensioning and tolerancing, who can and will explain this? I had a 2 week course on the standard ~ 20 years ago, but can't work with it.
Thanks;
joe b.

[Larry Gibson]

The potential for .013" clearance betwen the cartridge and headspace of the chamber is pretty much exactly what it means. It is only with the internet forums that some have cried "the sky is falling and we must tell the king" and many have believe "excessive headspace" is dangerous becuase it is written so. I have fired many, many cartridges in chambers that would be considered to have "excessive headspace" without problem. What is referred to as "excesive headspace" is in reality a non issue in most cases as you've discovered by your correct interprtation of the facts, though you don't want to believe it.

Larry Gibson

[45 2.1]

Excellent synopsis Larry.

[mike in co]

joe,
(i'm guessing you have a saami drawing, you do not specify)

look at the 308 win drawing, and you will see the same type of data.

if i was a manufacture of commercial ammo, i have the option of building my ammo to the large end of the spec. This would not be a good business decision because as anyone can see it is possible that this ammo MAY not fit all rifles. a little further digging and you will discover the government HEADSPACE measurement for 30'06 is not the same as the commercial.

and no the drawing does not show a 0.013 HEADSPACE.
The drawing clearly shows
HEADSPACE AS 2.0487 MIN 2.0587 MAX
( THIS IS CLEARLY MARKED AS HEADSPACE ON THE DRAWING).

a chamber with a HEADSPACE of 2.507 does NOT have a HEADSPACE of 0.002; it does have a HEADSPACE CLEARANCE of 0.002 more than MIN HEADSPACE.

you have been told before, by me and others that have common sense, that understand the difference between drawing deminsions and things called CLEARANCE AND INTERFERENCE is essential in commenting on drawings.

the drawings clearly show that between a MAX DESIGN HEADSPACE and a max cartridge there is 0.0061 CLEARANCE; that between MIN DESIGN HEADSPACE and a max cartridge there is 0.0039 INTERFERENCE and that with a MAX DESIGN HEADSPACE and a MIN cartridge there is 0.0131 CLEARANCE.
no where on the drawings is there a 0.013 HEADSPACE.

I'm surprised that a man of your intellegence, worldly knowledge, and prior firearms writing experience has such a hard time reading simple english.
if you cannot understand simple english, even when it has been explained to you,maybe you should refrain from writting and publishing on subjects you do not comprehend.

no, joe i do not KNOW why the powers that put these drawings together accepted a potential INTERFERENCE fit of .0039 for a MAX cartridge with a MIN HEADSPACE chamber. maybe they thought the manufactures would use COMMON SENSE and not build something that might cause an issue.

mike in co
added
trk brought up a point...i was a tool and operations planner/instructor for most of the 14 years i was in the aerospace/launch vehicle field....somewhere along the way we used ansi stds for dimensioning and tolerancing.

[Larry Gibson]

Joe

Perhaps a better understanding would be to ask ourselves "why is there headspace". The answer lies in firing pin protrusion. You see the firing pin must be able to smack the primer with suffiecient forse and DEPTH to make the cartridge go bang. Headspace tolerances of the chamber and cartridge simply allow that the cartridge case is held back far enough for the firing pin to hit the primer and make it go bang. It's as simple as that regardless of the witchcraft believed by some.

Larry Gibson

[Bass Ackward]

It's as simple as that regardless of the witchcraft believed by some. Larry Gibson


Wow. From experienced gun men.

Headspace establishes .... and controls .... the area from which brass can and will expand under tremendous pressure. The chamber itself is meant to "safely" support the brass during firing. Large headspace, causes an increasing gap between the barrel and the bolt from wear on the locking lugs which exposes a weak brass case and makes case seperation "a more likely possibility" in that area. Especially, as brass is fired over several times or in someone elses gun.

I have observed it or had it happen to me three times in my life. One the gun was destroyed in multiple pieces from self induced headspace from improper sizing as I observed. One incidence was simply unpleasant to the shooter, where the 223 military case had been fired in a riifle that obviously had headspace problems and was resized back into standard. And one case caused burn damage to my hand and face as the rifle was at fault for faulty headspace.

No Thank You, I want good headspace myself.

[Bass Ackward]

It's as simple as that regardless of the witchcraft believed by some. Larry Gibson


Wow. From experienced gun men.

Headspace establishes .... and controls .... the area from which brass can and will expand under tremendous pressure. The chamber itself is meant to "safely" support the brass during firing. Large headspace, causes an increasing gap between the barrel and the bolt from wear on the locking lugs which exposes a weak brass case and makes case seperation "a more likely possibility" in that area. Especially, as brass is fired over several times or in someone elses gun.

I have observed it or had it happen to me three times in my life. One the gun was destroyed in multiple pieces from self induced headspace from improper sizing as I observed. One incidence was simply unpleasant to the shooter, where the 223 military case had been fired in a riifle that obviously had headspace problems and was resized back into standard. And one case caused burn damage to my hand and face as the rifle was at fault for faulty headspace.

No Thank You, I want good headspace myself.

[Larry Gibson]

Bass

Double post must be an "emphasis"?

Three times? You must be pretty unlucky as I've had far more case head seperations than that with absolutly no damage to the firearm. Many many happened with 7.62 loads in M1a/M14s (well within headspace specs BTW) that had been loaded to many times with regular dies. I've also had numerous case head seperations in Mausers and '03s from cases that had been FL sized to many times. No damage from any of them. I've also fired many 7.62/.308s in '06 chambers, not excatly tight headspace there. All that happens is the case fireforms. That is unless you have a push feed and most often the case doesn't snap over the extracter and then it won't fire because the firing pin can't reach the primer. THAT is what happens if headspace is excessive with pushfeeds, most often they won't fire at all. If the extractor snaps over the rim then the case is held back well within tolerance and the shoulder will blow forward to fireform. Case head seperation can occur if the web has been thinned by too many FL sizings. However, with the bolt/barrel supporting the cartridge as it is supposed to (not like in your case) this is not dangerous but only a slight nuisance as you get a seperated case stuck in the chamber. A rather common occurance considering the number of broken shell extracors issued by the military and a like number sold to civilians. With CF the rim is held back by the extracter within tolerance and so the firing pin can hit the primer. The case then fireforms. Examples are the enlarged forward parts of .303 and 7.62R chambers. the case simply expand forward on firing. That is also why the Germans had a "field" headspace guage; the CF M98 extracter held the cartridge back to fire and it simply fire formed.

I would suggest there were other issues in your three incidents other than headspace problems. A case letting go because the bolt lugs set back exposing an unsupported area of the case has nothing to do with headspace; it has to do with the unsupported area of the case. Being unsupported it would have let go regardless if the headspace was correct or not. The simple fact is the case was not supported. I concur that firing rifles with unsupported cases as they are supposed to be is not a good situation. You do not provide enough information with the other two cases but I suspect the cause is also other than excessive heaspace. Just facts not assumptions (more PC than witchcraft I suppose as I refer to keep this a discussion as we've disagreed before).

Larry Gibson

[leftiye]

Fireform it, neck size it only, or full length size it without setting the shoulder back, forget it. Exception: self loading arms (full or semi auto, yes and some repeaters too) size shoulder just enough that chambering is easy (reads reliable), then forget it. Did I yet get worried if my gun's chamber was the size it was supposed to be? Not me.

This does not cover firing the wrong cartridge in a given gun, I know. That's up to you, just like sitting on dynamite to see if you'll survive it is up to you.

Headspace, or cardridge to chamber clearance is only semantics (which word you want to use), and only matters when you are making a new chamber, or measuring a chamber. In the first case, you make the chamber the way you want it. In the second case you either don't buy the gun, or reload accordingly.

You all reload, and probably all know this already. I know that shooters tend to be conservative etc., etc., but doesn't this topic remind you of orthodox religionists taking offense at someone who doesn't say it right? Previous thread on this subject went on and on (I won't say ad nauseum).

[trk]

We have a drawing of the 30/06 cartridge and chamber.
There's interference between the largest cartridge and the smallest chamber, and the smallest cartridge and largest chamber leafe .013" headspace.
I know just enough to know that this isn't what the drawing means.
Is there anyone here familiar with the ANSI spec/modern dimensioning and tolerancing, who can and will explain this? I had a 2 week course on the standard ~ 20 years ago, but can't work with it.
Thanks;
joe b.

You don't state the source or vintage of your drawing, so my comments refer to the SAAMI drawings published in the HANDLOADING book published by the NRA in January 1981; ISBN 0-935998-34-9 p276.

There is indeed an interference fit between the headspace dimension of the minimum chamber and the corresponding dimension of the largest cartridge. 2.0526 - 2.0487 = .0039".

Someone made the determination that when this much interference occurred it was OK. I've never measured a .004" crush fit on a cartridge but I'll guess that I could still close the bolt - testing would prove it one way or the other.

It does occur, but rarely, as the bulk of all the chambers will be nominal dimesion and the bulk of all the bullets will be nominal size.

This type of fit - a transitional fit - is common in many many manufacturing processes. It allows a closer clearance fit in the bulk of the matings of part a and part b. It does mean that in the odd occurance on the interference side that the parts will take more effort to put together. But it allows more reasonable manufactuing variation in both parts without having too loose a fit (albeit only occasionally) on the other end.

[trk]

ANSI standard Y14.5 is now ASME standard Y14.5. (It deals with dimensioning and tolerancing, latest LARGE revision was - I think - in 1994, a few minor revisions after). The M was added a few years prior to the 1994 edition to signify the addition of metric measurment. (It's on my desk at work, not here.) (OK, I taught it for 13 years and used is as a tooling engineer, but I can't remember everything.)

[joeb33050]

The potential for .013" clearance betwen the cartridge and headspace of the chamber is pretty much exactly what it means. It is only with the internet forums that some have cried "the sky is falling and we must tell the king" and many have believe "excessive headspace" is dangerous becuase it is written so. I have fired many, many cartridges in chambers that would be considered to have "excessive headspace" without problem. What is referred to as "excesive headspace" is in reality a non issue in most cases as you've discovered by your correct interprtation of the facts, though you don't want to believe it.

Larry Gibson

What is it that I don't believe? The .013", or that excessive headspace matters?
Please exploain.
joe b.

[joeb33050]

The drawing is from the NRA Handloading book by W. C. Davis.
Nothing above addresses the question. ANSI Y 1415M changed the way we dimension and tolerance drawings. It recognized the statistics involved in manufacturing. Drawings that would have been changed to eliminate interference fits under the prior system are now left alone and these interferences-to the untrained observer-are not.
I need somebody who knows, to explain the drawing.
Anyone?
Thanks;
joe b.

[Bass Ackward]

A case letting go because the bolt lugs set back exposing an unsupported area of the case has nothing to do with headspace; it has to do with the unsupported area of the case. Larry Gibson


Larry,

Don't understand how the double post happened. But this is the biggest safety issue discussed here. Far more dangerous than SEE or fillers or anything else.

Headspace is not permanent. The wear of the locking lugs is exactly why you get the increased brass / case exposure. That is how headspace changes. The warning is there because it can be very real if it sets up an SEE event. That's what blows the gun.

You could be right about the first two events. I can't proove it. I know the last case where I got burn't was a headspace issue because I tested the gun afterward. The gun was moderately new at the time 670 Win and apparently someone told this guy that lapping his locking lugs was a good idea and he never told me. Set the barrel back and the gun was fine.

But brass that is successfully fired in a poor headspace gun will be weak in the critical web area. Good headspace does not permit brass flow in that location. That's exactly why you get the warning of not to use brass that has been shooting cast for jacketed bullets at jacketed pressures. You risk a rupture.

[45 2.1]

But brass that is successfully fired in a poor headspace gun will be weak in the critical web area. Good headspace does not permit brass flow in that location. That's exactly why you get the warning of not to use brass that has been shooting cast for jacketed bullets at jacketed pressures. You risk a rupture.

It would be really nice to qualify some things when you say things like this. Too many people just read what has been written and accept it as truth when it is really on the edge of being untrue. Not everybody here has this problem. This so called "Headspace" issue is just poor reloading and nothing more.

[mike in co]

The drawing is from the NRA Handloading book by W. C. Davis.
Nothing above addresses the question. ANSI Y 1415M changed the way we dimension and tolerance drawings. It recognized the statistics involved in manufacturing. Drawings that would have been changed to eliminate interference fits under the prior system are now left alone and these interferences-to the untrained observer-are not.
I need somebody who knows, to explain the drawing.
Anyone?
Thanks;
joe b.

me thinks you have still missed the point.
the interference is between steel and relatively soft brass.
this is not a drawing about the bbl threads and the reciever threads. an interference fit would not work there.
a press fit part would have an interference fit in its design.
this is niether case. it is about wether or not a compressable object( a brass cartridge) will safely fit in a designed space.
the drawings work as they are, they need no explanation.

again

I'm surprised that a man of your intellegence, worldly knowledge, and prior firearms writing experience has such a hard time reading simple english.
if you cannot understand simple english, even when it has been explained to you,maybe you should refrain from writting and publishing on subjects you do not comprehend.
i think that your personal belief on what you believe"headspace" is , is clouding your view of what is being put in front of you.
its simple and its black and white.

mike in co

[Larry Gibson]

Larry,

Don't understand how the double post happened. But this is the biggest safety issue discussed here. Far more dangerous than SEE or fillers or anything else.

Headspace is not permanent. The wear of the locking lugs is exactly why you get the increased brass / case exposure. That is how headspace changes. The warning is there because it can be very real if it sets up an SEE event. That's what blows the gun.

You could be right about the first two events. I can't proove it. I know the last case where I got burn't was a headspace issue because I tested the gun afterward. The gun was moderately new at the time 670 Win and apparently someone told this guy that lapping his locking lugs was a good idea and he never told me. Set the barrel back and the gun was fine.

But brass that is successfully fired in a poor headspace gun will be weak in the critical web area. Good headspace does not permit brass flow in that location. That's exactly why you get the warning of not to use brass that has been shooting cast for jacketed bullets at jacketed pressures. You risk a rupture.


Let me explain it this way; had the case been fully supported as it was supposed to be and the chamber was deepened so there was "excessive headspace" then the case would have merely fire formed and not let go. The danger in your case was one of an unsupported case, not "excessive headspace". You want to believe the case let go because of "excessive headspace". The fact is the case let go because it was unsupported. It would have done that regardless of the headspace.

Larry Gibson

[Larry Gibson]

What is it that I don't believe? The .013", or that excessive headspace matters?
Please exploain.
joe b.

By this question it appears that you assume the .013" difference between the minimum cartridge dimension and the maximum chamber headspace is excessive headspace. It is not. You are comparing the dimensions of the cartridge with the dimensions of the chamber. The chamber has "headspace" measurements. The minimum to maximum dimensions of a cartridge must, by necessity, be smaller than the minimum headspace. This are safe allowable tolerances and have been since the inception of cartridge firearms. You assume the .013" difference to be an indication of "excessive headspace" when it is not.

You state in your original post; "I know just enough to know that this isn't what the drawing means." You are comparing apples with oranges and what you don't believe is the .013" tolerance between the apples and the oranges is safe and acceptable and not excessive headspace. Apparently from theprevious thread you did not get the grasp of "headspace". Consider that what you "know just enough of" is not correct and that your interpretation that there can be a .013" difference between the cartridge dimension and the chamber headspace is, in fact, correct and safe.

Larry Gibson

[Larry Gibson]

It would be really nice to qualify some things when you say things like this. Too many people just read what has been written and accept it as truth when it is really on the edge of being untrue. Not everybody here has this problem. This so called "Headspace" issue is just poor reloading and nothing more.

Now isn't that the truth, very good insight.

Larry Gibson

[Bass Ackward]

It would be really nice to qualify some things when you say things like this. Too many people just read what has been written and accept it as truth when it is really on the edge of being untrue. Not everybody here has this problem. This so called "Headspace" issue is just poor reloading and nothing more.



Bob,

Qualify how exactly? I don't understand what I would need to do after all that has been recorded and published. When the entire shooting industry supports a position and we have two guys disputing it, no one has asked you for proof. I gave examples that I personally have observed and one that could actually be identified by a measured means.

Forget headspace for a moment. When a powder in full case ignites, it ignites from the back. When pressure build and begins it's out press against the chamber it occurs where? The back where it is burning or the front? Brass on a taper flows what direction? Why are we recommended to discard cases after trimming so many times? Brass cases are heavier in the base because? So if we weaken the base area for any reason whether it be reloading fault or headspace fault, this is good or bad?

Headspace problems with reloaded cast cases are not because of the danger to me because I compensate. They fire form again. Otherwise you couldn't use improved or wildcat cartridges. But you can lose less cases in the fire forming process if you have minimum headspace instead of field headspace.

It's the uncontrolled expansion of brass that "can be" the problem. If you seat into the lands this poses little danger. If you want to say that as long as the case is held back by some reason whether that be from extractor or seating into the lands that you are OK. I agree. The problem becomes for those that don't have that option and or don't understand the few exceptions or the escape clause. Like the guy who lapped his locking lugs on a chambered firearm.

Larry,

Military gauges and inspections for long chambers are done upon manufacture. Not because chambers grow during storage. Not because a chamber stretches during firing or so many firings. The reason subsequent inspection is done is because of the wear. And the wear I described. And all wear in that manner enlarges the support gap. Period. If headspace is an infinite problem why do military field gauges stop where they do? Or why have one at all? Is military brass generally heavier than commercial brass? Why do you suppose? And in what area of the case is it heavier? How many times does the military reload it's brass compared to us? So headspace to the military can afford to be more generous. Especially when they might chamber dirty ammo. That's why the difference in standards from commercial sources. If the military had to reload over and over again, they would have a tighter headspace standard.

So if the military considers it important and all comercial industry does too, your incite is from?

[45 2.1]

Qualify how exactly? I would suggest you look at my byline that you have noticed before. I don't understand what I would need to do after all that has been recorded and published. Where? and by whom since several methods, not all of them suitable, are given. When the entire shooting industry supports a position The shooting industry is full on contridicting positions, as are all things in this world. and we have two guys disputing it, no one has asked you for proof. Yeah, but we just hate to see someone tout something like that. I gave examples that I personally have observed and one that could actually be identified by a measured means. Perhaps

Forget headspace for a moment. When a powder in full case ignites, it ignites from the back. When pressure build and begins it's out press against the chamber it occurs where? Entirely dependent on where in the pressure cycle it is. The back where it is burning or the front? Brass on a taper flows what direction? Again, this is dependent on where in the pressure cycle it is, especially with built in manufactureing tolerences. If you really want to contribute something here, tell us all the mechanics of what happens in a chamber that has maximum headspace when a bottleneck cartridge is fired in it. Why are we recommended to discard cases after trimming so many times? Well, from poor reloading practices, of course! How many shots do you get out of a case? I guarantee you that you get fewer than I do. Pope wore cases out in about 2800 shots, entirely due to the primer not staying in the primer pocket from wear of re and decapping primers. Brass cases are heavier in the base because? So if we weaken the base area for any reason whether it be reloading fault or headspace fault, this is good or bad? Again, weaking the base is from poor reloading practices.

Headspace problems with reloaded cast cases are not because of the danger to me because I compensate. They fire form again. People fireform in many ways, most damage their cases this way also. A point you didn't consider when asking why you shouldn't qualify what you said. Otherwise you couldn't use improved or wildcat cartridges. But you can lose less cases in the fire forming process if you have minimum headspace instead of field headspace. Do it right, except for faulty brass structure in a case, and it doesn't matter.

It's the uncontrolled expansion of brass that "can be" the problem. If you seat into the lands this poses little danger. Give this answer to 100 reloaders and you'll get a majority of them with thinned case webs. If you want to say that as long as the case is held back by some reason whether that be from extractor or seating into the lands that you are OK. I agree. I use neither of these methods. The problem becomes for those that don't have that option and or don't understand the few exceptions or the escape clause. Why don't you tell us where this is written, at least for the edification of the newbes. Like the guy who lapped his locking lugs on a chambered firearm. With good reloading practices, this wouldn't be a problem with any cartridge using the case shoulder as the datum for headspace, but a straight or belted case would cause a lot of problems.

BTW John, this isn't a flame. :)

[Bass Ackward]

From you? A flame? Come on ...... . And I don't worry about someone finding what I write credible here because I am safe spouting the .... party line.

An awful lot of money has been spent on research both civilian and military to improve headspace which is to say compensate for brass as the weak link in the chain. For some militaries that have heat problems with their automatics expanding in this area, they go to steel cases for added strength in case headspace goes.

As far as poor reloading practice goes you have a point .... but only to a point. Military ammo is beefed up and not intended to be reloaded. So headspace is not so much of a problem as it would be to a new or inexperienced reloader. And you have to go with the worst case senario. Right?

I Fire a SAAMI 06 round in my 03-A3 with a chamber that is just under the field No Go and then size it back to a SAAMI standard and you will have to trim. If you size it to work in dad's custom, you will have to trim even more. Doesn't matter what dies or proceedures you use, the brass flows forward to fill the chamber and causes thichening of the necks. Sized, they must be trimmed. Now you can make the argument why size and set the shoulder back, and then you have a point. "IF" the brass was fireformed in a push feed action under those conditions and then sized, you would soon see a bright ring forming around the case just above the base where head seperation would occur eventually. Would that matter what reloading procedures you used? I don't think so.

P.O. Ackley sought to end brass flow forward and created straight sided cases. There is minimal brass flow anywhere after fire forming. The idea to improved cases is that the straight walls can take higher pressures without brass flow. Less bolt thrust to cause wear. And a shaper shoulder from which to establish better, longer lasting headspace.

Example: Two 7X57s were made back to back from the same reamer. One was chambered to just close on a Go guage. Mine was chambered to a factory 7X57 case and won't even begin to close on a go gauge. Which has better brass life and has never had a case failure fire forming? Mine. The only brass I have for it is the origional cases fire formed in 1972. Loads run up to 70,000 psi and mine are still tight even in the primer pocket area. I guarantee you Pope was never pushing that kind of pressure for 2800 rounds. My only problem was keeping out the donut that formed until the brass stabilized and evened out. I had to ream until it stopped. Same origional brass. How many firings? I truely wish I could quote you a number but I'd be lieing if I did. I got no idea, but nothing else comes close.

The Army liked the concept of improved cartridges so well that it developed and standardized the first mass produced, improved cartridge known as the 7.62 NATO or the 308 Win. No relaoding practices are involved here, so reloading is and cn not be a factor. Please pay attention to the last propaganda line even though pressure for the military round is 12,000 psi less. :grin:


This is from Wikipedia 308 History under Development:

http://en.wikipedia.org/wiki/7.62_%C3%97_51_mm_NATO

The military 7.62x51mm cartridge is nearly identical to the commercial .308 Winchester. NATO controls specifications for the military round while SAAMI controls specifications for the civilian round. The organizations have established two differences: the standard pressure is 50,000 psi for most military rounds, while the SAAMI maximum is 62,000 psi for the civilian round. The NATO M60 High Pressure Test round is loaded to a pressure of 67,500 psi, so military arms should be capable of handling the pressure of civilian rounds[1]. The military chamber is specified to be 1.645 inches, compared to the civilian chamber of 1.632 inches. Though this difference is just 0.013 inches,[2] a chamber of acceptable military length will put excessive stress on the thinner civilian brass, causing premature head separation.

[felix]

John, that's why BR chambers are cut so "tight" up against the brass. Those cases can be reloaded until the barrel is gone, not gone for the BR guys, but for us only needing 1/2 inch accuracy. 10,000 rounds of 75K pressure each, for only about 25-50 cases total. That is case life. I anneal my necks after about 30 reloads because I don't like the harder sizing through my hand held dies. I have never had a neck split. 22/40 = 222 ackley at 40. ... felix

[Larry Gibson]

Bass Ackward

Not wanting to get in the middle of this but I'd like to ask a couple questions;

I've been studiying military ammunition for many, many years and this is the first time I have heard; " For some militaries that have heat problems with their automatics expanding in this area, they go to steel cases for added strength in case headspace goes." Every reference I've read refers to steel case production as a cost saving measure since mild steel is much less expensive than brass. Question; what is your source for this astounding new piece of news?

"I Fire a SAAMI 06 round in my 03-A3 with a chamber that is just under the field No Go and then size it back to a SAAMI standard and you will have to trim. If you size it to work in dad's custom, you will have to trim even more. Doesn't matter what dies or proceedures you use, the brass flows forward to fill the chamber and causes thichening of the necks." Question(s); Are you sure the brass flows forward to fill the chamber? Couldn't it be that the bass actually flows forward in the FL sizing die because the sides of the case are squeezed in and the brass has to go somewhere so it flows forward? When FL sizing and the sides of the case are sized in and the brass flows forward doesn't the shoulder move forward and then get set back as the case is pushed completely into the FL die? Isn't it then that the brass flows from the should which is getting set back into the neck causing it to thicken? When bottle neck cartridges are NS'd doesn't that alleviate the brass flow problem?

"P.O. Ackley sought to end brass flow forward and created straight sided cases." Having read PO's books several times I was under the impression he straightened out the case sides to increase case capacity and to decrease bolt thrust. Question; Could you show me where in PO's book I have missed the part about straight sided cases being to decrease brass flowing forward?

"There is minimal brass flow anywhere after fire forming." I've delt with a number of wildcats and improved cases over the years. Even when set up so the case is a crush fit when the bolt is closed many cases actually shrink in OAL length when fire formed as the brass flows out to fill the chamber space it many times pulls brass back in from the neck. Question; could you explain why the brass does not flow forward?

"Example: Two 7X57s were made back to back from the same reamer. One was chambered to just close on a Go guage. Mine was chambered to a factory 7X57 case and won't even begin to close on a go gauge. Which has better brass life and has never had a case failure fire forming? Mine. "

When a FL sized rimless cartridge is fired it is pushed forward in the chamber until it is stopped by the shoulder of the chamber. This can be by the firing pin or by the ejector. The pressure expands the cartridges sides and they grip the walls of the chamber. When pressure rises above 40,000 psi or so the head of the case is pushed back against the bolt face. The brass stretches in the web area as the sides of the case still grip the chamber walls. The brass of the cartridge case actually "flows" back not forward if you want to call it that. FL resizing the case with regular dies will not swage this stretched brass in the expansion ring back into the original thickness of the web. The brass at the expansion ring gets pushed (flows) forward necessitating trimming and can result in incipient head seperation after a several firings. In the case cited above you negated the space between the bolt face and the head of the cartridge so there was no stretch of the brass in the web area of your cases. This is the same thing we accomplish by NSing only to get longer case life. Question; Were you aware that this is what happens?

"The Army liked the concept of improved cartridges so well that it developed and standardized the first mass produced, improved cartridge known as the 7.62 NATO or the 308 Win." Question; Are you aware of the 7.65 Belgian/Argentine and the .300 Savage? You may want to take a hard look at their design?

"No relaoding practices are involved here, so reloading is and cn not be a factor. Please pay attention to the last propaganda line even though pressure for the military round is 12,000 psi less. :grin:"

Wikpedia is renowned for it's inaccuracies (anyone can post anything there) and it is inaccurate in this case. I will post the correct pressure figures from the TM; Small Arms Ammunition, published by the arsenals as they should know, when I get home tonight. Question; why the "grin"?


Larry Gibson

[mike in co]

308 win vs 7.62x51 nato pressures:

308 win
MAP 62000 PSI( MAX AVERAGE PRESSURE)
MPSM 66000 PSI ( ...DONT HAVE THE EXACT...BUT MAX PRESS SINGLE......)

PROOF PRESSURE
MIN 83000 PSI
MAX 89000 PSI

US ARMY 7.62X51( NOTE DOES NOT SAY 7.62 NATO)

MAX 50,000 PSI
PROOF 67,000 PSI

THE M852 MATCH 7.62 ROUND IS SET AT 50,000 PSI WITH 42 GR OF IMR 4894
THE M118 SPECIAL IS SET AT 50,000 PSI WITH EITHER 44 GR WC846 OR IMR4895
THE M993 AP ROUND IS SET AT 55,115 WITH BOFORS NC1290....THIS ROUND IS LISTED FOR USE IN M60 AND M240 MACHINE GUNS AND THE M24 SNIPER RIFLE.

NIETHER SPEC LISTS THE METHOD OF MEASURING PRESSURE...AND JUST HAVING NUMBERS IS A DANGEROUS THING...........

HOPE SOMEONE CAN ADD TO THIS....

[felix]

Larry, the sharp shoulder for a case like an Ackley design is supposed to stop the foward flow of brass. In reality, with pressures greater than say 40K CUP, you have to thin the necks in a tight fitting chamber, and most especially the "donut". The configuration of the sidewalls prolly has nothing to do with brass movement after being fireformed well. Yes, under these circumstances, the brass does flow foward, and foward only. But it soon stops after some sort of normalization to the load being shot. It will start moving again as soon as the load is increased, even somewhat slight. ... felix

[Larry Gibson]

Regards 7.62 Nato vs .308 Win

Let's go to the horses mouth; TM 9-1305-200, Small-Arms Ammunition published by the Army Arsenals which developed the 7.62 NATO cartridge of which Winchester introduced the civilian version states:

Regards M80 Ball; "The average chamber pressure may vary from 45,000 psi to 65,000 psi depending on the temperature."

Further, the "average pressure" is stated to be a +/- 7,000 psi figure.

Now if we consider the published "maximum" allowable pressure for the .308 is most often in the 62-68,000 psi range we see that if we compute in a +/-7,000 or so psi (which is pretty close to the industry standard then it is obvious there's no real difference between the 7.62 NATO cartridge and the .308 Winchester pressure wise. As a matter of fact a friend who has an Oehler M43 tells me that most of the commercial .308 Winchester ammunition he's tested has bee below the pressure of most U.S. M80 Ball he has tested. I know this is contrary to the usual intenet hype on this subject but hey, since when did facts get in the way of hype or the so called "facts" of Wikpedia.

Larry Gibson

I might add that since 1967 I have fired many thousands of 7.62 Nato rounds in .308 chambers and quite a bit of .308 in 7.62 Nato chambers (many in M14 chambers BTW). In that 40 years I have never had so much as a twinkling of any indication of any pressure problems or not one single case of head seperation on thefirst, second or third firing.

[waksupi]

You guys are giving me the fantods!

[Larry Gibson]

Larry, the sharp shoulder for a case like an Ackley design is supposed to stop the foward flow of brass. In reality, with pressures greater than say 40K CUP, you have to thin the necks in a tight fitting chamber, and most especially the "donut". The configuration of the sidewalls prolly has nothing to do with brass movement after being fireformed well. Yes, under these circumstances, the brass does flow foward, and foward only. But it soon stops after some sort of normalization to the load being shot. It will start moving again as soon as the load is increased, even somewhat slight. ... felix

No problem with that felix, but what Bass is talking about is what leads to incipient case head seperation and what you mention isn't it. It is as I described above.

Larry Gibson

[Larry Gibson]

I'll have to bow out of this conversation at this point. I leave at O dark 30 in the morning for Camp Lajeune once again to train Marines. Seems strange an old Army dude like me training Marines but they aren't really different than soldiers, damn good Americans all. The tactics are the same where they are going and I'm proud to be able to help. I shall return, didn't some Army guy say something like that;-) on 20 February and should re-enter the net.

Cast well, hold hard and shoot straight.

Larry Gibson

[waksupi]

Larry, thanks for your service. It is good the old dogs, can still teach the young ones some tricks!

[Bass Ackward]

Larry,

Boy you get around for a reservist. Must be the MAN.

I can not find the article on steel. The point was as the actions heated under automatic fire, steel expands when heated and can take minimal headsapce and push it passed the limit. The steel was a strength benifit at this point. You were right on the other cartridges. I knew of the 300 Savage and forgot.

All,

What I find strange in this discussion is how as gun men and military men we are taught safety all the time. Everything from shooting glasses to pointing a weapon can say that one safety factor is over hyped. Headspace is not a bugaboo. Its a safety factor to support the brass case so that as reloaders and industry can reproduce a reliably safe product. Key word there was safe.


Bob / Larry,

You asked would I describe the internal ballistics in a case. Sorry can't. But let's look at the 223 case failure. This was the one where no real damage occurred other than a gas vent.

The bullet was lodged in the barrel at the failure just into the bore. The failure in the case was a 1/8th" cut just above the head. About 1/2 of the powder did not ignite. So it seems possible to me .... that had that reduced powder charge of slow powder been re-ignited with the bullet lodged in the bore, that could meet the definition of an SEE event. That is what we suspect on the gun (6.5 Rem Mag and factory ammo) that discintigrated simply because of the delay, click bang involved. The case let go, chicken or the egg. Could brass failure lead to increased chances for SEE? But there was nothing left to prove. Regardless of the reason, unsafe and unsettling events that have me wanting as much case support as I can get. The 223 did have tight headspace by the way.

Bob's point about neck sizing is valid as long as the case didn't flow from where it wasn't supposed to from the start. Fire forming to a straight sided case is one thing. Brass flow is mostly out. The tighter the headspace, the less forward you have. Fire forming a tapered case in a long chamber resulting from poor headspace will result in brass flow mostly forward. It has too to fill. When it did, then it was already weakened and neck sizing is immaterial to case strength or life. Military brass is thicker and can accomodate this stretch for one firing.

Felix,

I know about the method I used to build that 7X57AI. Both cartridges were loaded using the same set of dies for quite awhile, but my brass, purchased from the same lot as his, shooting very much the same loads, annealed by he who taught me, is still around. Pretty much as close to an example without an actual test as I could make. Your point of brass life for benchrest guns is why I did that. Brass is still the weak link in the firing chain.

[uscra112]

Let's get back to the GD&T issue shall we guys?

What EXACTLY are the callouts that the gentleman refers to, IN DETAIL? I don't see those anywhere in this discussion.

You can get a manual of the Y14.5 standard from ANSI, for a fee, or you can probably find it on the internet for free, or fire up a copy of AutoCAD.

Now, in the US auto industry, where I happen to work with dimensional gauging equipment, we speak of a tolerance as an absolute OUTER LIMIT, and the process engineers try like hell never to exceed 25% of it. In fact, they'll stop the line if some feature on a part exceeds 25% of tolerance. Which is why American engines and trannys are so much better than they once were. It also means that something like 85% of the production will be within 25% of tolerance, and only 0.01 percent will exceed tolerance.

I'm sure that's true for cartridge makers and barrel chamberers too. Just because you've got a loose tolerance doesn't mean you should be sloppy about it.

It may also well be that those 30-06 tolerances were set loose so wartime production could run faster with fewer stoppages. Remember the 30-06 goes back to a long time before statistical process control.

And the risk of an occasional blown cartridge has to pale in comparison to the risk of combat in general, wouldn't you say?

[trk]

Let's get back to the GD&T issue shall we guys?

What EXACTLY are the callouts that the gentleman refers to, IN DETAIL? I don't see those anywhere in this discussion.
...



Compare the two dimensions used to establish 'headspace/head clearance':

2.0526-.0070 and
2.0487 min 2.0587 max

From Davis' book (NRA publication) HANDLOADING published in 1981:
(which means the notations are pre-1982 ANSI Standard Y14.5.

http://www.hunt101.com/img/473381.jpg

[joeb33050]

I sent this question out to some friends and some folks in the gun,ammo,reloading industry. Two responses, both say that the dimensions and tolerances are as they look. One says that the .004" interference will keep the gun from closing on the cartridge, the other says that the .004" interference can be easily overcome by a bolt action rifle.
Still waiting, hope I'm wrong.
When was the last time you couldn't get a factory cartridge into a fairly new factory gun?
joe brennan

[45 2.1]

Bob's point about neck sizing is valid as long as the case didn't flow from where it wasn't supposed to from the start. Fire forming to a straight sided case is one thing. Brass flow is mostly out. The tighter the headspace, the less forward you have. Fire forming a tapered case in a long chamber resulting from poor headspace will result in brass flow mostly forward. It has too to fill. When it did, then it was already weakened and neck sizing is immaterial to case strength or life. Military brass is thicker and can accomodate this stretch for one firing.

I spoke of either good or poor reloading practices, not the above, part of which will get you in trouble if you adhere to that method.

[joeb33050]

Compare the two dimensions used to establish 'headspace/head clearance':

2.0526-.0070 and
2.0487 min 2.0587 max

From Davis' book (NRA publication) HANDLOADING published in 1981:
(which means the notations are pre-1982 ANSI Standard Y14.5.

http://www.hunt101.com/img/473381.jpg

I think/hope that the drawing notes hold the secret. One note is "All calculations apply at maximum material condition(MMC)"
Another note shows an X in a circle = headspace dimension, there are two dimensions with this symbol, the other is the .375 Basic shoulder diameter.
joe brennan

[joeb33050]

Compare the two dimensions used to establish 'headspace/head clearance':

2.0526-.0070 and
2.0487 min 2.0587 max

From Davis' book (NRA publication) HANDLOADING published in 1981:
(which means the notations are pre-1982 ANSI Standard Y14.5.

http://www.hunt101.com/img/473381.jpg

I think/hope that the drawing notes hold the secret. One note is "All calculations apply at maximum material condition(MMC)"
Another note shows an X in a circle = headspace dimension, there are two dimensions with this symbol, the other is the .375 Basic shoulder diameter.
joe brennan

[mike in co]

Joe,
what secret ??? no slaming, no flaming.

the two drawings are separate, but complimentary.

one is the specs for chamber, one is for cartridge.

yes there is a potential interference.

my first reply shows the math of the numbers.

what secret ??

mike

[trk]

I think/hope that the drawing notes hold the secret. One note is "All calculations apply at maximum material condition(MMC)"
Another note shows an X in a circle = headspace dimension, there are two dimensions with this symbol, the other is the .375 Basic shoulder diameter.
joe brennan


Let's walk through the numbers.
First, the note: All calculations apply at maximum material condition (MMC).
a) MMC condition for the cartridge is the LARGEST cartridge.
b) MMC condition fot the chamber is the SMALLEST chamber.

The dimensions are as follows:
Therefore, the headspace dimension (circle X) goes from the bolt face to the datum (diameter .375") which is also marked headspace dimension and note B which says "BASIC". (That means it has NO tolerance, it is exactly a diameter of .375") which shall fall on the inside slope next to the neck which shall be 2.0487 to 2.0587" from the bolt face WHEN the chamber is at it's smallest (MMC). It could be argued that the 2.0487" IS when the chamber is at MMC and that the MMC dimensions include the diameters.

The cartridge is similarly dimensioned to a 'basic' dimension of a diameter of .375" which can range from 2.0526" to .0070 less (2.0456")

SO, head clearance can range from the largest chamber - smallest cartridge to the smallest chamber - largest bullet. (We've gone through the math before.)

Futher one would EXPECT that most chambers and bullets to be produced not at the extremes but in the middle of the normal ranges of production.

FWIW

[BAGTIC]

Steel cases were introduced as a means of conserving strategic materials, not because of strength.

'Improving' cases as by Ackley improves ballistics primarily by increasing powder capacity. Larger capacity accomodates more powder therebye increased velocities with minimal increase in pressure.

ACKLEY DID NOT HAVE PRESSURE TESTING EQUIPMENT. THEREFORE HIS EXPLANATION SHOULD BE TAKEN WITH A CUP OF SALT.

There are gun design limits to maximum acceptable pressures, whether the case holds or not. Anyone who is depending on a cartrige case's adherence to the wall to restrain bolt thrust is playing a fool's game. First the cross sectional area of the cartridge case at the head is so modest (.0443 square inch in a .308 case) compared to the chamber area that the effect would be minimal. Even if the brass held 80,000 psi the .04435 s.i. area would only hold 3,544 pounds in tension. That is far less than standard round to round pressure deviation.

Brass does not flow towards the neck because of pressure. If it did it would also occur in straight cases.

What happens is that the thinner brass near the front of the cartridge adheres to the chamber wall before the thicker and stronger case head has expanded enough to cling to the chamber walls. The rising pressure pushes the cartridge base back, stretching the case length, until it is stopped by the breech. Stretch a piece of metal and it becomes thinner. This thinning occurs forward of the thickest part of the case head at the location, from the base, where the brass first becomes thin and weak enough to yield.

Neck thickening occurs when this case which has been expanded, fireformed, to maximum chamber dimensions is reduced by the sizing die. When the now larger case is swaged down the brass flows forward, the only direction it has to go, just like the core of a swaged bullet. That is how the new dies that 'prevent' case lengthening work. They dont give the brass anywhere to flow.