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Old December 28, 2018, 08:51 PM   #1
Bucksnort1
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Headspace

Now here is a topic I'll bet has been beaten to death over the years.

I watched a You Tube video explaining head space. The video was well done and used a cut away bolt action rifle with (probably inert or maybe its ert, who knows) what looks like a 30-06 cartridge. I am not an expert at the subject but I now understand what it is but what is confusing me is what it's called.

Why is it called headspace?
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Old December 28, 2018, 09:20 PM   #2
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Space from the case head to the face of the closed bolt; head space
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Old December 28, 2018, 09:42 PM   #3
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Quote:
Headspace is one of the most critical measures in your rifle. A quick definition: the distance from the face of the locked bolt to a datum line or shoulder in the chamber that arrests the forward movement of the cartridge. The term originated when all cartridges had protruding rims, so the measure was initially taken only at the head. Now it includes other spans.
From Gun Digest
Case head is explained better by a drawing. Hopefully it is attached.
Attached Images
File Type: jpg The-Cartridge-Case-3.jpg (30.8 KB, 61 views)
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Old December 28, 2018, 10:20 PM   #4
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Yes, I know the anatomy of a case so I know what the head is. The way the video explained, it has nothing to do with the case head but rather, chamber fit. I attached the link to the video.

https://www.youtube.com/watch?v=vAgjvBxzng4
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Old December 28, 2018, 11:12 PM   #5
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The "head"space originally applied to rimmed cartridges, and was literally the clearance dimension for [drumroll please] the case head.
See http://www.nucem.se/images/guns/hand...574570head.gif

Then we invented modern rimless cases and messed everything up .. . .
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Old December 29, 2018, 02:24 AM   #6
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I will make one post then run away.Yes,OP,it has been beaten to death.Use your "search " function.You will find plenty to read.

I don't care to do this again right now.
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Old December 29, 2018, 09:28 AM   #7
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But when the rifle is fired, the ejector and or the firing pin push the case into the chamber as far as it will go. Where it stops directly affects reliability. This was a big issue before precision machining. The amount of headspace and firing pin protrusion directly impact how solidly the primer is whacked when shooting.

Therefore, firing pin protrusion, headspace and primer seating are all critical dimensions in the modern rifle.

As a reloader, headspace becomes a control point on the case side. Controlling the datum to case head measurement as well as primer seating is critical to accuracy and reliability.
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Old December 29, 2018, 10:14 AM   #8
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HiBC,

Chill a bit. No one is forcing you to do anything relative to this posting. I don't want an explanation of what head space is, I want an explanation of why it's called head space and not chamber space or some other more appropriate name. Based on some other descriptions, I have been under the impression headspace is the distance between the face of the bolt and the head of the case.


BiBC
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Old December 29, 2018, 10:18 AM   #9
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HiBC,

I took your advice and did a search on head space, just now. Perhaps I'm not working the "search" properly but I come up with nothing.
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Old December 29, 2018, 11:14 AM   #10
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OK hot shots: at the upper end of the cartridge, is the case mouth, neck, and shoulder. So why is the head at the other end??

I say it should be called the foot. Then we can argue about foot space!
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Old December 29, 2018, 11:26 AM   #11
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The current terms and definitions according to SAAMI are:

HEAD CLEARANCE
The distance between the head of a fully seated cartridge or shell and the face of the breech bolt when the action is in the closed position. Commonly confused with headspace.

HEADSPACE
The distance from the face of the closed breech of a firearm to the surface in the chamber on which the cartridge case seats. 1. BELT: A type of chamber design in which the cartridge seats in the chamber on an enlarged band ahead of the extractor groove of the cartridge body. 2. MOUTH: A type of chamber design in which the cartridge seats in the chamber on the mouth of the cartridge case. 3. RIMLESS: A type of chamber design in which the cartridge seats in the chamber on the shoulder of the cartridge case. 4. RIMMED: A type of chamber design in which the cartridge seats in the chamber on the rim or flange of the cartridge case.

HEADSPACE GAUGE
A device used in a firearm to determine the distance between the breech face and the chamber surface on which the cartridge seats. Also called Breeching Plug.



Now if you want to go back 80 years, in 1937 Phil Sharpe described "headspace" as what SAAMI now defines as "head clearance."
But by the 1949 revision/addendum to 'Complete Guide to Handloading' he had gone over to the present usage.
So there is a little history for you.

I will further note that F.W. Mann described his "Hamburg Rifle" as having no headspace/head clearance/"backleash" because its interrupted thread locking lugs "screwed the breechbolt right up to the head of the cartridge."

Target shooters used to like the Ballard single shot because it could be fitted to zero head clearance with a particular lot of ammo.

Me? I think it best to just take "headspace" as a term of art and not worry about its etymology.

If you just must, you will get a lot of verbiage from F. Guffey's posts.
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Old December 29, 2018, 12:24 PM   #12
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I was surprised.Searching "Headspace" was useless.Try "headspace defined"

The argument always comes down to this.The "headspace" of a firearm is established during manufacture. Its about using headspace gauges to represent and control the dimension from the breech face to the feature in the chamber the cartridge stops against. "headspace" is totally about the firearm itself,it is established and measured independently from ammunition.

You can pull any firearm off any rack and check headspace using only headspace gauges.

OP,I agree with you that functionally what we are often concerned with,especially when reloading,is "head clearance",as defined above in the excellent and useful post #11


A condition of excess or insufficient "head clearance" may exist in any firearm that is absolutely perfect in "headspace".


"Headspace" is about the gun. "Head Clearance " is about the ammo.,or more correctly,the fit of the ammo to the chamber.We can have an out of spec chamber and custom handload ammunition to ideal "head clearance"

To further confuse the issue,we can buy "Bushing type cartridge headspace gauges",that we can use to check that,regardless of the firearm,our handloads have been made to SAAMI "headspace" ? lengths....but I have commited a sin because I applied the term "headspace" to ammunition. IMO,there is the criteria of having a SAAMI spec firearm.
There is the criteria of handloading ammunition that meets SAAMI specs,that should work with SAAMI tolerances and work fine in any SAAMI spec chamber. I'm a heathen in that I commit the crime of referring to that concept as "Cartridge headspace" (In fairness,the cartridge does not have "space" It occupies space.)
Then there is "head clearance"which is what we might be functionally concerned with,to minimize case stretch and extend brass life. (Unless we are loading ammo to fit several rifles,or commercially reloading.)

We have two further issues to deal with.One is language,terminology,semantics,etc. The term "Cartridge headspace" is regarded by many as intolerable,because it is technically incorrect.


IMO,its useful in the explaination of the concepts .I'm wrong.


The other issue is what happens when we try to discuss this topic. The search of "headspace defined " will perhaps shed light.We get into the swamp,the weeds,folks who use the extractor as a headspace datum feature,etc,etc,etc,etc.

Last edited by HiBC; December 29, 2018 at 12:36 PM.
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Old December 29, 2018, 12:49 PM   #13
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Jim Watson,

I was concerned that members like Guffey and Unclenick (no disrespect intended, Guffey and Unclenick) would respond with the equivalent of two or three chapters from an encyclopedia.

HiBC, I don't need to do any searching. You have hit the nail squarely on the head. What I learned from the You Tube video, is this is all about the gun chamber.

Thanks.
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Old December 29, 2018, 12:51 PM   #14
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Jim Watson,

Thanks for the excerpts from SAAMI. I think many of us (I am an "us") have been confused by terminology.
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Old December 29, 2018, 12:52 PM   #15
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Jim Watson,

Thanks for the excerpts from SAAMI. I think many of us (I am an "us") have been confused by terminology.

HiBC, just for grins, I searched on "headspace defined" and found nothing. I'm sure it's there somewhere but, as I said, I'm ok with not searching.
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Old December 29, 2018, 01:38 PM   #16
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Headspace dimension (chamber) is:
- The distance from the bolt face to the chamber point that stops the case from entering (be it the rim, the belt, or the mid-point shoulder)

Headspace dimension (case) is:
- The thickness of the rim (or) the distance from the case head to the front of the belt (or) the distance from the case head to the mid-point shoulder -- again whatever stops the case upon entry.

Both dimensions have manufacturing tolerances (±) that are 'supposed' to functionally mesh in action**
As an engineer, that's I care to know, need to know, and/or use in the real world.


(Take it away Guffey !!!)









** Notwithstanding that pesky real world again:

Last edited by mehavey; December 29, 2018 at 01:46 PM.
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Old December 29, 2018, 01:43 PM   #17
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I am, like many, guilty of referring to "cartridge headspace" because it is easier to say or type than "head to datum dimension."

You just have to go with the term of art approach.
The no. 1 dictionary definition of headspace is "The volume above a liquid or solid in a closed container. " That does not help the reloader much.
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Old December 29, 2018, 01:55 PM   #18
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"...the ejector and or the firing pin push the case..." No, they don't.
"...The amount of head space..." Head space is a rifle manufacturing tolerance that allows ammunition from all manufacturers to be used in a like chambered rifle.
"...why it's called head space..." It's literally space for the head of the cartridge. Where it's measured from(isn't actually measured by head space gauges. Those only tell you if the head space is within tolerance.) is different according to the type of case.
"...As a reloader..." Cartridges do not have head space. Hence reloading has nothing to do with it. Nor can you adjust or fix bad head Space by doing anything to the case.
Do not get your education via You Tube. Read some books.
As much as I dislike using Wikipedia as a source, their article on head space is pretty good. https://en.wikipedia.org/wiki/Headspace_(firearms)
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Old December 29, 2018, 02:10 PM   #19
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And in practical application, Wiki is wrong:

"Head space is a rifle manufacturing tolerance that allows ammunition from all manufacturers to be used in a like chambered rifle."
[Wrong -- See image Post#16 ]

"...As a reloader..." Cartridges do not have head space."
Wrong again -- Cartridges do have a headspace dimension. Ignore that at your peril. Again See Post#16 ]

"Nor can you adjust or fix bad head Space by doing anything to the case."
Wrong again. You may adjust/match [case] headspace dimension to [chamber] headspace dimension and all is right in the world. [just keep the two together.]

It always bothers me when priests invoke the "Doctrinal Religion of Headspace" to say that your own "Head" space can't apply itself to both understanding and solving a problem.
(But I guess that requires a PhHD [doctorate of headspace philosophy] to apply]
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Old December 29, 2018, 04:46 PM   #20
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Bucksnort`:

I hope this is not taken wrong, everything has to be called something.

We live in a country called America not Columbus because someone gave him credit (and we can segue to the Native Americans who call it Turtle Island)

Unlike the classification of plants animals etc there is not standard other than what gets invented at the time a term is needed.

So, when cartridges were invented and a name was needed it got settled on head space.

One of the few documents we have good info on is the US Constitution as they kept great notes on the arguments (Federalist papers) as well as extensive writing by most if not all the participants.

Things get names for various reasons by various methodology.

Its as good a name as any and as long as we (?) understand its a chamber relationship with the bolt head (or rim to chamber) good enough.

Granted a lot of arguments about its so called mis use.

I contend as long as we understand what its under discussions and its relevance, that is fine.

In my world we tend to get down to some very detailed specifics. To me a Unit Injectors is a whole world apart from an Injection pump and there are two types of injection pumps as well as breakdowns in the one type of plunger injection pump.

In that case I would not dream of calling a Unit injector a nozzle because the parts guy is going to twist his brain and try to figure out what I am talking about and what I want.

Generically I can talk about diesel engines and injector systems and any mechanic will understand that. That is where we are as re-loaders in head space. We don';t need to understand the datum and crosses of lines that define the shoulder point that makes it (you can be arbitrary and come up with other spots on the shoulder to define it).

What we do know is that its an important piece of information and we have gauges to check it and ways to check the cases we size to ensure they work with that (or a number of chambers)
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Old December 29, 2018, 06:19 PM   #21
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Can you explain yourself? I know the terms and interactions between components, so I would like for the benefit of my own growth to know what I am saying wrong, if you know.

Quote:
Head space is a rifle manufacturing tolerance
It is never expressed as a tolerance. It is always expressed as a dimension....with a tolerance

Quote:
"...As a reloader..." Cartridges do not have head space. Hence reloading has nothing to do with it. Nor can you adjust or fix bad head Space by doing anything to the case.
What do yo you call that dimension then? If we agree that the case fits in the rifles “headspace” dimension, what should we call that dimension? It is on every SAAMI dwg for the chamber and case. On the chamber side, it gets a symbol designating it as the headspace dimension. What is it called on the case side? I just want to know so I don’t take a 9 page beating every time I or anybody else discusses fitting the case accurately within the rifles actual headspace dimension... Also, you could teach Hornady too because they call it case headspace and sell a tool to measure it.

Quote:
Do not get your education via You Tube. Read some books.
Are you insulting me, the university that gave me a degree in engineering , anybody with an engineering degree, how should I take this?
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Old December 29, 2018, 06:32 PM   #22
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Relax.
Us engineers won the Reformation away from the Priests of the Holy Headspace back in the day.
(Not that there aren't some diehards)
The rest is history.. . . .
<BSEG>




(postscript: See Post#19)
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Old December 29, 2018, 08:33 PM   #23
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Quote:
will make one post then run away.Yes,OP,it has been beaten to death.Use your "search " function.You will find plenty to read.

I don't care to do this again right now.
Same could be said of 99% of what we discuss on here.
We still enjoy discussing it.
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Old December 29, 2018, 08:37 PM   #24
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Quote:
"...As a reloader..." Cartridges do not have head space. Hence reloading has nothing to do with it. Nor can you adjust or fix bad head Space by doing anything to the case.
You obviously have never done any wildcatting. You most definitely can compensate for headspace by reloading.
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Old December 29, 2018, 08:43 PM   #25
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@mehavey....enjoying your sense of humor....I guess I should read more and post less!
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