Headspace in non-belted rifle cases
- Thread starter Bucksnort1
- Start date
I prefer to full length size bottleneck cases so there's between 1 and 2 thousandths head clearance on the chambered round. Any more means too much case stretching in the shoot-resize cycle which leads to short case life. Any less and the chances of the bolt binding due to out of square case heads and bolt faces increases which is a sure cause of accuracy degradation.
I want a little head clearance so the extractor can push the back end of the case against the opposite chamber wall. If this is done the same way for every shot, best accuracy's at hand. One reason why many folks get better accuracy with new cases than neck only sized ones that have grown in headspace enough to bind the bolt when chambered.
As best I can tell, this is what most benchresters started doing a few years ago. They set their fired bottleneck case shoulders back about .001" in full length sizing dies with necks a tiny bit smaller than loaded round neck diameters to meet the above objectives. This method also makes the straightest case necks on case shoulders aligned with the body axis.
From what I glean from benchresters, their tiniest groups are still the same small size, but their biggest ones are a lot smaller. Which is why most of them quit using any neck only sizing routine with fired cases. Other competitive disciplines learned this decades ago. So did other disciplines. But there'll still be some who won't make the change.
I want a little head clearance so the extractor can push the back end of the case against the opposite chamber wall. If this is done the same way for every shot, best accuracy's at hand. One reason why many folks get better accuracy with new cases than neck only sized ones that have grown in headspace enough to bind the bolt when chambered.
As best I can tell, this is what most benchresters started doing a few years ago. They set their fired bottleneck case shoulders back about .001" in full length sizing dies with necks a tiny bit smaller than loaded round neck diameters to meet the above objectives. This method also makes the straightest case necks on case shoulders aligned with the body axis.
From what I glean from benchresters, their tiniest groups are still the same small size, but their biggest ones are a lot smaller. Which is why most of them quit using any neck only sizing routine with fired cases. Other competitive disciplines learned this decades ago. So did other disciplines. But there'll still be some who won't make the change.
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Gunplummer
New member
BartB seems to have a grip on headspace. Picher, if you resize your brass to fit your chamber, and it does not fit someone else's chamber, it is a wildcat. I may be wrong(Not), but where does a reloading book recommend neck sizing brass from your rifle and jamming it in your Buddy's rifle? Chambers have tolerance and it is possible to neck size brass and not have it fit in 5 different guns. If you do not follow SAAMI specs, and this includes brass manufacture, it is a wildcat. I am pretty much out of gun work now, but a few years back SAAMI sent me updates on chamber specs. A lot of them were accepted "Wildcats" for years being submitted by small companies, but SAAMI would not certify them until they were totally tested and given a definite tolerance. The drawings were for "Reference only". I have "Cheated" and made new bolts to bring guns back into "Headspace", and the brass did resize like butter, but I would bet the body angle of the chamber was off or oversize to begin with. Things are rarely cut and dried with guns.
Nooooo. Once again the concept of SAAMI chamber headspace tolerances for all rifles, and an individual case's headspace dimension is confused.
Rifle manufacturers cut their chambers to within SAAMI headspace tolerances (which can be ± 0.004" in some instances.
Ammunition manufacturers size their cases to the smallest SAAMI dimension to ensure fitting in all rifles -- regardless SAAMI's ± tolerance.
A case that's been resized to some specific dimension within that tolerance, but doesn't fit someone else's specific rifle of that same cartridge, is still a "30-06". It just means that there's an engineering tolerance mismatch between two parts. It is not a wildcat which is deliberately designed to be totally outside those tolerances.
Gunplummer
New member
That is ridicules. Once you have to force a cartridge into a chamber, it is out of SAAMI specs. If you have to force a case into your chamber, and it will not go into battery in a different gun, it is not to specs. I used to test fire guns I made a new reamer for by removing the extractor. The first couple rounds are not in a hot gun. You should be able to stand the gun up straight on the table, give it a slight tap on the table, and the fired brass will fall out. Most times the brass fell out just by inverting the rifle. You should also be able to drop a loaded cartridge in, close the bolt (With no extractor) and have that cartridge fall out. I worked with a man that retired 30 years in the Corp and then worked as a civilian in depot gun repair. A bad .50 came in and this guy started beating on it. The old guy stopped him and said "If you have to force it, something is wrong". I am a firm believer in that statement to this day.
Yes, it is. The only "spec" is the chamber.
If one wants to call being sized to absolute minimum chamber dimensions so that it will go into any chamber -- irrespective of that chamber being long or short within the SAAMI span -- then call it what it is: "Full-Length Resized to Minimum Dimensions" But that's all.
According to SAAMI's .308 Win. specs in:
http://www.saami.org/PubResources/CC_Drawings/Rifle/308 Winchester.pdf
...a case with 1.633" headspace is within specs.
...a chamber with 1.630" headspace is within specs.
That case won't easily fit that chamber.
Gunplummer, does your claim allow for tolerances? Or is it based on base spec numbers alone?
http://www.saami.org/PubResources/CC_Drawings/Rifle/308 Winchester.pdf
...a case with 1.633" headspace is within specs.
...a chamber with 1.630" headspace is within specs.
That case won't easily fit that chamber.
Gunplummer, does your claim allow for tolerances? Or is it based on base spec numbers alone?
Bucksnort1
New member
Headspace
Mehavey, I watched a reloader on You Tube correct a sizing problem (couldn't get the bolt closed) for .308. He demonstrated the problem with cases he resized then, he showed how he screwed down the resizing die just a bit more than recommended, which solved his problem. Does this sound right to you?
Mehavey, I watched a reloader on You Tube correct a sizing problem (couldn't get the bolt closed) for .308. He demonstrated the problem with cases he resized then, he showed how he screwed down the resizing die just a bit more than recommended, which solved his problem. Does this sound right to you?
Pogy, all that does is ensure the resizing die actually stays in contact with the shellholder when the ram is fully raised -- instead of "springing" a few thousandths above that because of resizing stress on on the press.
Then the sizing die gets to do what it was designed for: size the case to (ostensibly) minimum SAAMI chamber specs.
Then the sizing die gets to do what it was designed for: size the case to (ostensibly) minimum SAAMI chamber specs.
I could have worded this better.
That is one strong statement, no equivocating about that, unsupported case heads (case head protrusion) have nothing, absolutely nothing, nada, zlich, zero, to do with headspace.
I would have to disagree with that assessment. Decades ago minds more brilliant than any here came up with a system so simple that a trained monkey could assemble, maintain, safety check, a firearm, given that the monkey used the parts, tools, gages, and followed the procedures provided to him. The SAAMI headspace definition is a good one, but leaves out a lot of assumptions that the monkeys don’t need to know as long as they do what they are told without thinking much about it. But, the monkeys are interpreting the world based on the gages and sizing dies they have without any overarching understanding of what is going on.
This reads as though case head protrusion is similar to the question “where are the cows in the pasture”. It is not something you can really specify with any exactness as in a couple of minutes the cows will be someplace else, and 10 minutes hence they will be will be in a random location and the whys and wherefores unintelligible to the human mind. So, is cartridge protrusion sort of like where the cows are in the pasture?: random, no exactness, a metaphysical concept ?
Brian Pfleuger
Moderator Emeritus
Well... that post is an excellent F. Guffey imitation, I'll give you that much. Otherwise, I don't know what to make of your examples.
I will only say again that the unsupported part of the case is unrelated to headspace and is entirely dependent on the design of the barrel and bolt rim/extractor.
For .308Win, as an example, SAAMI specifies no chamber dimensions whatsoever for the area between the boltface and 0.200" forward.
One could design a gun with no bolt rim and no extractor, having the head of the case exactly flush to the end of the barrel with no unsupported area whatsoever or alternatively could leave 0.200" between the bolt and start of the barrel, leaving that 0.200" completely unsupported, and have the same exact headspace.
Cartridge protrusion is a physical thing but it is not, and is not related to, headspace.
I will only say again that the unsupported part of the case is unrelated to headspace and is entirely dependent on the design of the barrel and bolt rim/extractor.
For .308Win, as an example, SAAMI specifies no chamber dimensions whatsoever for the area between the boltface and 0.200" forward.
One could design a gun with no bolt rim and no extractor, having the head of the case exactly flush to the end of the barrel with no unsupported area whatsoever or alternatively could leave 0.200" between the bolt and start of the barrel, leaving that 0.200" completely unsupported, and have the same exact headspace.
Cartridge protrusion is a physical thing but it is not, and is not related to, headspace.
Guffey's posts sometimes reads as though he wrote them while sleep walking. Even if written somnambulating, I am proud of Guffey: he actually knows the importance of case head protrusion. I would never send a rifle to be barreled by a guy who thought it was something that was inexplicable.
So, for this generic rifle, is that 0.200" unsupported plus or minus a thousandth, or 0.200 plus 0.500"? Just how much of the case head can be unsupported?
Brian Pfleuger
Moderator Emeritus
Slamfire said:
The 0.200" measurement is designated as Basic, which means that it theoretically has 0 tolerance.
I think it's rather disingenuous to alter the argument from one of whether or not case head protrusion is equivalent, or even related to, headspace to one of "actually know(ing) the importance of case head protrusion".
The importance of it is another matter entirely. It is not headspace and is not related to headspace. Two different guns with different bolt rims/extractors and/or differently drilled chambers can have different headspace and different amounts of case head protrusion and the protrusion and headspace are not related to each other in any predictable way.
It is fact that they are unrelated. A given gun could have 0.200" of case head protrusion and 1.630" headspace or it could have 0.000" case head protrusion and 1.630" headspace. The case head protrusion could be anywhere between 0.000 and 0.200" and the headspace would be completely and totally unaffected.
I am certain in some types of actions the case could be completely supported, except that without room for an extractor, it would require a ram rod or cleaning rod to knock the case out. But that is really not the issue, few shooters want a cartridge gun that is barely faster to reload than a muzzle loader.
So, given that headspace is the distance forward of the bolt face, just how much of the case can be left out of the chamber?
Brian Pfleuger
Moderator Emeritus
How does one design the bolt face and extractor?
Have you ever examined an Encore? The extractor is built into the barrel. The case is essentially fully supported. A bolt gun could be designed similarly, maybe there is one, I don't know.
In any case, the limit is essentially how thin can the extractor and/or bolt rim be made as each has to perform it's function?
I am not that concerned about the maximum amount of case head support, but rather the minimum and the effects thereof.
I am quite certain the headspace was correct in these pistols, that is the breech face to shoulder dimension, but there was another issue creating Glock blowups.
A good discussion can be found here:
http://www.thegunzone.com/glock/glock-kb-faq.html
http://www.thegunzone.com/glock/kb-notes.html
Brian Pfleuger
Moderator Emeritus
Yes, the issue creating those blow ups, I maintain, was that Glock wanted to beat SW to market with the first 40SW pistols, and they did.... but they did it by modifying an existing design, rather than designing a true 40SW frame.
The result was unacceptable feed ramp geometry, other dangerous feed ramp intrusion into what should have been supported case, farther up than the web extends. Glock went with unacceptable feedramp intrusion. 40SW kBs are the result.
BTW, it's quite likely that the headspace was NOT correct on those cases. It rarely is on semi-auto handguns. The only tolerance is the free play in the extractor slot. If the brass is shorter than the chamber headpace dimension by more than the play in the extractor, the case will "headspace" on the extractor. That is a very common condition.
The result was unacceptable feed ramp geometry, other dangerous feed ramp intrusion into what should have been supported case, farther up than the web extends. Glock went with unacceptable feedramp intrusion. 40SW kBs are the result.
BTW, it's quite likely that the headspace was NOT correct on those cases. It rarely is on semi-auto handguns. The only tolerance is the free play in the extractor slot. If the brass is shorter than the chamber headpace dimension by more than the play in the extractor, the case will "headspace" on the extractor. That is a very common condition.
How do you have one without the other? Like flight without air or drag. Back to basics:
The system was set up so trained monkeys could drop gages into firearms. As long as the monkeys don’t start grinding off material someplace, use the proper cartridges, case head protrusion is something that the monkeys don’t need to know anything about. If the firearm swallows the field gage, the monkey knows that something is wrong and has been trained to go to higher authority for issue resolution. Something I have noticed, simians are interpreting the world based on their headspace gages and sizing dies. Guess what, they were not told that when they are gaging headspace with their plug gage, case head protrusion is the most safety critical measurement of all.
What is likely to happen when a rifle swallows a field gage? One is that the case sidewalls over stretch causing a “case head separation”. That is primarily a function issue if the case head separation is within the chamber. If, as what appears to be happening with the Glocks, if it occurs outside of the chamber, a catastrophic failure occurs.
Legalistic argument, hiding behind definitions behind which you do not understand either the assumptions or implications.
Why should I believe this?, and, even if it was off, where was it off?
And that is not case head protrusion?,