Help me understand "Head Space"

This is the way I think about it.

A cartridge can only go so far into an open chamber. Imagine you take your gun apart (it's easy with a pistol) and you have the chamber in your hand and you drop a cartridge into the chamber. It will only go so far because something stops it from going too far in. On some rifle cartridges like a .223 REM or .30-06 it is the shoulder of the case, thus I have heard people say that those cartridges head space off of the shoulder. Now, I don't know if they should say it that way, but I hear it all the time. A .22 Long Rifle stops going in when the rim of the cartridge contacts the ledge in the chamber. A 9 mm stops going in when the edge of the case mouth (right next to the bullet) contacts an edge inside of the chamber.

All of that to describe dropping a cartridge into an open chamber. Now let's close the chamber so to speak. In a bolt action rifle, that would be closing the bolt. Now remember the head of cartridge is the end where the primer / makers mark / caliber are located. Once closed, the head space is the distance between the closed bolt's face and the head of the cartridge. A perfect fit would mean there is no space, the bolt's face is touching the head of the cartridge.

Now imagine a .223 cartridge where it was resized incorrectly and the shoulder was mashed down from the case mouth towards the case head. Now, when you drop this cartridge into the chamber and close the bolt there is a space between the bolt's face and the case's head. At some point too much space between the bolt face and the case head become an issue.

Imagine a 9mm cartridge where the case was trimmed too much and now the case / brass is shorter than it should be. When it goes into the chamber and the slide closes there is space between the case's head and the breech face.

That is the way I think about it.
 
Once closed, the head space is the distance between the closed bolt's face and the head of the cartridge.
Click to expand...

NO ! that is incorrect . Using your analogy , head space is the distance from the bolt face to where the cartridge was stopped from going in any further . 223 bolt to chamber shoulder , 9mm bolt to ridge in chamber that the case mouth stops on , 22lr is the same as all rimmed cases . This measurement ONLY pertains to areas in the chamber or between the bolt face and where a rimmed cartridge stops and has nothing to do with the cartridge it self . So on a 223/30-06 the head space would be the distance from the closed bolt face to the area of the CHAMBERS shoulder where the case would have stopped . This area of the chambers shoulder is the datum line/area . There is no line but many say line when referring to this area .
 
Then what is the space between the case head and the bolt face called?

Am I missing something? I don't know.

I am talking about reloading, not setting up a rifle or re-barrelling a rifle. This means that I am working with a rifle that has been properly setup and has had the space measured from the bolt face to the point in the chamber that is used for stopping the forward motion of a cartridge.

If you resize your case incorrectly and push the shoulder back to far, what have you messed up? The head space? So, again, what is it called when you do this? The space between the bolt face and the head of the case, what is that called?
 
LOL.

Here is why I said what I said, I have two reloading manuals. Speers #14 and Hornady 8th.

From Speers, page 87:

"Remember that most bottleneck cases headspace on the shoulder. With the proper die setting, the shoulder will not be pushed back past its original position. Pushing the shoulder beyond this point will create excessive headspace."

From Hornady page 15:

"As the firing pin strikes, it moves the case forward to contact the front of the chamber, giving a little headspace -- but not a dangerous amount."

So, with all of the statements that head space is the distance between the breech face and the point in the chamber used to stop the forward travel of a case and that it is fixed is contradicted by the statement that you can create headspace from these two reloading manuals.

The Hornady manual shows a picture of the gap between the bolt face and the case head and indicate that to be the created head space.

So, if it can be created by setting the shoulder back too much, then the cartridge does have something to do with it.

If one thing is for sure in my mind, the term is used in two different ways in my reloading manuals.
 
Last edited:
Here is an online resource, for those that don't have the same manuals. The author designates two types of head space. Chamber headspace and cartridge headspace length.

http://www.massreloading.com/bottleneck_case_resizing.html

Before we get into setting up the sizing die, we need to discuss headspace and cartridge headspace length. Headspace in a firearm is defined as the distance from the breech or bolt face to the part of the chamber that stops the forward movement of the cartridge when it is inserted into the chamber... The cartridge headspace length is the distance from the case head to the part of the case on which the cartridge headspaces...

The difference between the chamber's headspace and the cartridge headspace length determines the amount of extra fore-and-aft 'room' the cartridge has in the chamber... Too much room (because the cartridge headspace length is too short for the chamber) can result in inconsistent ignition, poor accuracy, short brass life, or catastrophic case head separation. In other words, if you get the cartridge headspace length wrong, the ammo will not shoot at all, will shoot badly, or will blow up. Therefore, it's quite important to get the cartridge headspace length right.
Click to expand...
 
Here is another online article that I just "re-found". I read it a while back.

http://www.larrywillis.com/headspace.html

"The term headspace means the "space" between the "head" of your case and the breech. This space (clearance) is set when your barrel is installed. Handloaders should minimize the chamber clearance that their handloads have in their chamber."
 
And one last one, which again distinguishes cartridge headspace.

http://www.sinclairintl.com/.aspx/lid=16134/GunTechdetail/Setting-up-a-Full-Length-Sizing-Die-

"Cartridge Headspace and Over Sizing
Cartridge headspace can be defined as “how much the cartridge case moves forward and backward in the chamber upon firing when the breech or action is fully closed”. When a chamber is reamed by a manufacturer or gunsmith, there are maximum and minimum dimensions that SAAMI (Sporting Arms and Ammunition Manufacturer’s Institute) specifies for the chamber for a particular cartridge. This dimension determines the fixed headspace of the rifle’s chamber.... Excessive sizing will also allow your brass to chamber easily but will create excessive headspace. This extra headspace will allow the case to have excessive forward and backward movement when it is fired...."
 
Last edited:
Those reloading book quotes are saying the same thing in different ways. The Speer quote is merely telling you to not set the shoulder back too far when you resize it. If you do, the case (when fired) will stretch more than you want it to. You will have put a case that is shorter (from base to shoulder) than desired. When fired it will stretch to fill the chamber, and work the brass more than would be desired. That will lead to case head separations eventually. I know this from experience. The Hornady quote is saying the same thing in a different way. The case with the shoulder set too far back will move forward with the firing pin strike, the powder will ignite and the case will stretch and fill the chamber. So don't set the shoulder too far back. Adjust your sizing die to set the shoulder back just enough that the round will chamber without noticeable resistance.

That's about the best I can do to respond to your question.

Where's BartB? He loves stuff like this.
 
Larry Willes is wrong . Not only that but technically there is no such thing as case/cartridge head space . Now most if not all hand loaders use the term anyways excluding Mr Guffey . If you look at the SAAMI specs the is no term for the length of the cartridge from head to datum point
 
Those reloading book quotes are saying the same thing in different ways. The Speer quote is merely telling you to not set the shoulder back too far when you resize it. If you do, the case (when fired) will stretch more than you want it to. You will have put a case that is shorter (from base to shoulder) than desired. When fired it will stretch to fill the chamber, and work the brass more than would be desired. That will lead to case head separations eventually. I know this from experience. The Hornady quote is saying the same thing in a different way. The case with the shoulder set too far back will move forward with the firing pin strike, the powder will ignite and the case will stretch and fill the chamber. So don't set the shoulder too far back. Adjust your sizing die to set the shoulder back just enough that the round will chamber without noticeable resistance.

That's about the best I can do to respond to your question.
Click to expand...

Thanks.

I get what it is talking about, I am just pointing out that they call it head space.

What I have learned from this is that there are two types of headspace, if you will.

The headspace that is set when the chamber is fixed to the action and is measured from the closed bolt face to the point inside the chamber. This headspace is fixed / constant so to speak.

Cartridge headspace is how well the cartridge fills the chamber headspace. Setting the shoulder back too far creates cartridge headspace which is indicated by the space between the bolt face and the head of the cartridge when the cartridge is as forward as it can go.
 
Larry Willes is wrong . Not only that but technically there is no such thing as case/cartridge head space . Now most if not all hand loaders use the term anyways excluding Mr Guffey . If you look at the SAAMI specs the is no term for the length of the cartridge from head to datum point
Click to expand...

Is the Hornady and Speer manuals wrong as well? They clearly state that headspace can be created.
 
They say head space can be created . They don't say that space is the head space measurement . If a case is sized really short you can have excessive head space as well . The thing about all this is you MUST understand what the actual definition of head space is . You then can incorporate the term in other areas of reloading and most will understand what you're talking about . I know it sounds complicated but as long as you except there is only one true head space measurement the rest will fall into place .

Let's ask this , how do you check head space ? And what are you measuring . Do you use a sized cartridge or a gage that is set at a industry standard measurement .

How about this ? Let's say you have a chamber that head spaces .020 larger then the SAAMI maximum . You then size a case that fits tight in the chamber . Does the chamber have excess head space ? Interesting right
 
Last edited:
Wow! I thought I explained that, sirgilligan. Go to post number 2 by Unclenick and read and reread the first sentence. Read it till it makes sense.

Yes, you can 'create' headspace. If you oversize the case, or in other words if you set the shoulder too far back. You have created headspace. If you set the shoulder back like Goldilock's porridge, it'll be just set back enough and not too much, and will be just right.

As for how much to set the shoulder back, it will depend on your rifle's chamber. Some are roomy and some are snug. For my 220 I have to resize the case as much as the press, die, and shellholder will allow. The chamber in the Douglas barrel is very snug. For a Ruger I once had, the chamber was rather roomy and I didn't want to resize the case more than necessary, which would have created excess headspace, so I'd lightly set the shoulder back on the case which had been fireformed to my chamber.
 
So back to the original post:

Loaders:
I think I don't understand what "Head space" is.
Help.
Live well, be safe
Prof Young
Click to expand...

How does anyone know which head space he is referring to?

Is it the chamber head space, or the head space that is created by making a case too short?

These are rhetorical questions, but maybe the OP would care to answer.
 
Well, there are too many books and online sources that perpetuate the definition that I submitted. I may be wrong, but I have lots of company. :D

http://www.gundigest.com/headspace-101-what-happens-inside-your-rifles-chamber

"Altering case dimensions changes the relationship of the cartridge to the chamber. Reducing head-to-datum line length of the round can result in a condition of excess headspace, even if the firearm checks out perfectly."



http://www.redding-reloading.com/tech-line-a-tips-faqs/145-dealing-with-headspace

"Headspace is one of those concepts that is both very simple and yet is extremely important to achieve gilt edged accuracy. For bottlenecked cartridges, headspace is simply the distance between the head of the cartridge case (the end where the primer is inserted) and the front/face of the firearm's bolt when the case's shoulder is positioned against the front of the chamber.... Headspace is like Goldilocks porridge. It has to be just right for the best accuracy. Too much is bad and too little is also bad. "

From the Forster Products Headspace Gage Instructions:
"Headspace is the distance between the face of the breech and the base of the cartridge when the action is closed."
 
Last edited:
You must log in or register to reply here.
Back
Top