Confused about Headspace

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haskins02

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I am a relative newbie to reloading and will soon begin reloading .308 Win for a Browning X-bolt. There is only one reloading aspect (so far) that confuses the heck out of me: HEADSPACE.

First, it is confusing because there are so many different definitions for it. Examples:

Definition 1: The fit of a cartridge in a chamber measured as the distance from the bolt face to that part of the chamber which stops the case’s forward movement (for .308, it’s the shoulder). Note: this is a measurement of the CHAMBER.

Definition 2: The distance from base of the cartridge case to that part of the case that stops its forward movement (for .308, it’s the datum point along the shoulder, .400 inches in diameter). Note: this is a measurement of the CARTRIDGE, not the chamber.

Definition 3: The distance between the bolt face and the datum. Note: this is a measurement of the chamber AND the cartridge, because the bolt face is one end of the chamber and the datum is on the cartridge.

All of these definitions are DIFFERENT. So do you see why I’m confused? Can anyone clear this up?

Second, I am confused because I don’t know WHY I need to worry about headspace anyway. I will not be reloading for competition, just informal target shooting and hunting. The best accuracy I expect to achieve is 1-inch groups or slightly less. I will pay attention to maximum cartridge OAL. I will be using a factory produced rifle (Browning) and factory produced dies (Lee). So, can anyone clarify why I need to worry about headspace, and how I would go about solving any “headspace problems”?

Thanks.
Greg
 
In simple terms headspace is the area (front to back) in the chamber not filled by the case. .308 headspaces on the shoulder, so if there is too much slop (sized/pushed the shoulder back too far creating artificial headspace) you can get into trouble when firing it.

The firing pin pushes the loose round forward until the shoulder of the case hits the shoulder of the chamber. It fires and expands the forward third of the case in the chamber, gripping the chamber walls and sealing off the chamber (so hot gases don't go rearward, out of the action). Then the case stretches until the case head is stopped by the breech face (bolt). If it has to stretch too far it can thin excessively near the case head, and in a worse case scenario, separate, letting loose hot high pressure high speed gases out of the action where they can wreak havoc. :eek:

So, can anyone clarify why I need to worry about headspace
Click to expand...
It is a safety thing.

It also can extend brass life by limiting it, but first and foremost it is a safety thing.
 
From a reloading standpoint, the less headspace you have, the longer your rifle brass will last before it is stretched to the breaking point.

You can have a perfect rifle, and perfect brass, and have perfect headspace.
And then push the shoulder back too far during sizing and create excess headspace yourself.

SO it pays to understand it well enough to avoid doing it!

You can avoid doing it by adjusting your sizing die until the bolt just closes with slight resistance on a sized case.

Heres more then you want to know!
http://www.brownells.com/.aspx/lid=...g_Success_-_Minimum_Headspace_and_Maximum_COL



rc
 
You mean my simple explaination is wrong? Head space. The headspace is the area between the cartridge head and the bolt face. The smaller (to a point) the better.
 
As far a reloading you do not have to worry about head space unless you are loading for a belted magnum and even then under special sizing issues.
 
Static headspace dimension:

The linear distance between the bolt/breechface and the cartridge stop heading.

Cartrides use 4 different methods of obtaining headspace. Rimmed cartridges headspace on the rim. Bottleneck cartridges headspace on the shoulder. Belted cases headspace on the belt. Straight-wall autopistol cases headspace on the case mouth. (For simplicity's sake, I'll use straight walled pistol cases that headspace on the case mouth.)


Dynamic...or working headspace is the difference between the static dimension and the length of the case. F'rinstance...If a .45 ACP chamber length is .910 inch and the case is 895 inch...the pistol has .015 inch of headspace when that cartriege is fired in it.
If the next case is .890 inch long...the headspace is .020 inch, and so forth.

Static headspace is fixed and only changes with wear. Dynamic headspace changes with every round fired unless they are all trimmed to exactly the same length.
 
As far a reloading you do not have to worry about head space unless you are loading for a belted magnum and even then under special sizing issues.
Click to expand...

I'd have to disagree strongly with this statement with what I'm experiencing with my 03 Springfield. My dad used to reload rounds for me and some of those rounds didn't fit real well. Somebody mentioned above a 'quick and dirty' method of sizing the case until the bolt closes with just slight resistance. Now that I have my dads' reloading press and I'm starting to reload myself, that's exactly what I'm having to do IN SPITE OF case lengths that are within parameters, and OAL's that are within spec. In other words, rounds can be loaded where the cartridge and bullet measure out just fine and should work, but the bolt won't close. Headspacing seems to be the problem and sizing the brass to the rifle seems to be the solution.
 
As far a reloading you do not have to worry about head space unless you are loading for a belted magnum and even then under special sizing issues.
Click to expand...
I'd have to disagree strongly with this statement
Click to expand...
Me too.


In other words, rounds can be loaded where the cartridge and bullet measure out just fine and should work, but the bolt won't close. Headspacing seems to be the problem and sizing the brass to the rifle seems to be the solution.
Click to expand...
Yep. Cartridge O.A.L has nothing to do with headspace. As long as it is short enough to not jam into the lands, that won't stop it from chambering.

A piece of brass that is too long from the base to the shoulder will. That is a headspace problem of another kind. Too little, well no, headspace. You have to have some.

I'll add "Artificial headspace" to Tuners "Static" and "Dynamic" headspace. It is created when we push a shoulder back to far on a bottle necked cartridge (such as .308), or trim a straight walled auto case too short.
 
If you think (reloading)Belted Magnums should only head space "on the belt"...you will soon be in for separated cases. I've saw more magnum cases separated than any other type case!

Jimmy K.
 
I think Boots Obermeyer nailed it when he said "it's a relationship between case dimension and chamber dimension". Speaking of bottleneck cartridges, there are standard chamber dimensions for each cartridge as it relates to factory ammo. When reloading ammo, an excessive headspace condition can be created by bumping the shoulder back too far, and then there is the negative headspace condition created by not bumping the shoulder back far enough that generates so many "why don't my cartridges fit" posts on THR.

Don
 
"All of these definitions are DIFFERENT. So do you see why I’m confused? Can anyone clear this up?"

Yeah. First, forget the technical definitions. All that only matters to the gunsmiths who are cutting chambers.

For reloaders, it's enough to say headspace is simply the effective room for the cartridge to fit into your chamber. If the cartridge is too large, the "headspace" is too small and you can't close the bolt on the round. If the cartridge is too small, the fit will be loose, a rattle fit. Neither condition is good. Reloaders need to make their cases the correct size to fit what ever headspace the chamber has.

Pushing a case fully into a sizer is supposed to form it back within normal SAAMI specs altho sometimes it doesn't quite work out that way; the sized cases may be too small or too large, depending on the actual die tolerances. But who cares if their ammo will fit into every rifle ever made in that caliber! Most of us only want our ammo to fit OUR rifle, and to fit it right.

Full length case sizing should be carefully aimed at trying to get the case to fit snugly, with the least amount of excess (head) space possible, and still be able to chamber it without difficulty. We don't get that by simply sitting the sizer down until it touches the shell holder and happily resizing away.

Start sizing with the sizer die a full quarter turn OFF the shell holder and check that the cases either won't chamber or will only do so with some difficulty.

Turn the die down in 1/16th turn increments on a fired case. That's about .004" or about half of the full normal maximum total headspace range. Some folks have said turning a die down a quarter turn at a time is a "small amount", actually it's a HUGE amount of difference, about twice the full tolerable range of case headspace! Turn your size die down NO MORE than 1/16th of a turn, or even less when you get close, for each chamber test step. This sizing method applies to all bottle-neck cases, rimmed, rimless and belted, there's no difference in the application.

Size a case at each step, try to chamber it and keep working the die down gently until the empty cases chamber right. Lock the die there, that's the correct case fit for your rifle's chamber. That's what headspace is really all about.
 
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I'll add "Artificial headspace"
Click to expand...

A good point, and one that should be addressed. Although adjusting headspace by adjusting the sizing die and using the case shoulder to reduce it does create a minimal or zero headspace condition...it doesn't provide safe headspace in rifles that have worn or deformed locking lugs and/or lug recesses.

A method used by pistol shooters is to seat a shouldered lead bullet farther out so that the shoulder jams into the rifling lands instead of headspacing on the case mouth. Again...this reduces working dymanic headspace, but doesn't correct for an excessive headspace condition.
 
Size a case at each step, try to chamber it and keep working the die down gently until the empty cases chamber right. Lock the die there, that's the correct case fit for your rifle's chamber. That's what headspace is really all about.
Click to expand...

Great technique. I would add the tip to perform each incremental adjustment on separate cases. Once you find the 'right' adjustment, go back and size the first few samples. Repeated sizing on the same case often means you still need to adjust the dies after finding what you think is the right adjustment. Springback, work-hardening, not sure exactly what's going on but I have seen it happen too often to discount.
 
As a practical matter, some amount of head clearance must be present to assure reliable operation and chambering. In most modern rifle chambers using SAAMI spec ammunition, Head Clearance will be something on the order of four to six thousandths (.004" to .006") of an inch.
As you can see, head clearance is actually the difference between the headspace measurement and the case/cartridge (for rimless bottleneck cases -as measured from the case head to the datum on the case shoulder). As such, it is entirely possible to have Head Clearance problems in a firearm that has correct headspace, if the ammunition is improperly resized. It is also possible to experience these same problems with ammunition having the proper SAAMI specs, if the headspace of the firearm is out of specifications. Head Clearance problems can frequently be corrected by proper die adjustment, but any suspect ammunition or firearms should be checked by a competent gunsmith. While the condition may be corrected or compensated for, cases that have developed signs of incipient head separations must be destroyed and scrapped at once.

Here are some quotes from SAAMIs glossary -

"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.

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."
Click to expand...



Referring to headspace as anything to do with a case I believe is incorrect
because Headspace is a characteristic of a chamber (not a case, or ammunition).
Headspace is specified on the SAAMI chamber drawing (and not on the cartridge drawing).

There are minimum and maximum chamber dimensions... (the rifle makers use) - Headspace.

There are minimum and maximum cartridge dimensions... ( the die makers and ammo makers use) - Which effect Head Clearance - (Commonly confused with headspace).


From Sierra (I don’t agree with Sierra’s use of headspace ) but here it is -

Full Length Sizing

Full length sizing is the most commonly used form of resizing. Full length sizing dies reduce the neck and body dimensions of a fired case to allow free and easy chambering. In most instances, full length sizing will reduce the case dimensions enough to allow it to be used interchangeably in several different rifles chambered for the same cartridge. Contrary to popular opinion, full length resizing is commonly used by the vast majority of competitive shooters, especially in those disciplines where rapid-fire is involved. It should be clearly understood that full length sizing does not reduce a fired case to its original, unfired dimensions. The goal here is to bring the case dimensions down far enough to allow the reloaded case to be chambered without difficulty.

Adjustment of the full length die calls for the die body to be screwed down in the press until it contacts the shell holder at the top of the ram’s stroke. If the ammunition is to be reused in the same gun the cases were originally fired in, back the die off 1/2 to 3/4 of a turn and size a lightly lubricated case. Wipe the case dry, and chamber it in the gun. If any resistance is felt, lower the die body another 1/8 of a turn (or less), and repeat the process with another fired case. This is repeated until the action will just close without resistance. When this has been accomplished, set the lock ring to secure the die in place. This method will ensure that the fired cases are resized with a minimum amount of headspace. This case has now been “custom fitted” to that particular chamber.

This will normally provide the best case life and accuracy, but does require that the ammunition only be used in the gun in which it was originally fired. If the ammunition is to be used in a different gun of the same chambering, of course!, the sizing die should be adjusted down until it just contacts the shell holder at the top of the ram’s stroke.

This results in a slightly greater amount of headspace, but will allow the ammunition to be used in several different guns. Whichever adjustment style is used, full length sizing is generally the best sizing method for most shooting situations.
Click to expand...
 
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Greg,
You are correct. It is confusing. And I see it used in text in all three ways. But, your three definitions do not contradict the spatial relationship between cartridge and chamber with bolt closed and locked. I think you understand that relationship by reading your post, and that is the main thing.

For rimless bottleneck cases and the associated chambers, one needs some clearance axially. But, too much can lead to case stretching and shortened life.
 
With my grandsons, my son, my ex son-in-law and myself, we sometimes have 6 same caliber rifles in the field at the same moment. We resize for the smallest chamber so our rounds are interchangeable. Yes, it is harder on the cases,but we can exchange ammo if needed. If you only use the ammo for one rifle, try to keep the sizing to just the neck for longer case life.
 
JimKirk said:
If you think (reloading)Belted Magnums should only head space "on the belt"...you will soon be in for separated cases. I've saw more magnum cases separated than any other type case!
Click to expand...

I thought this was odd too. I use a Redding Instant Indicator Comparator to check the headspacing on my .300 Win Mag cases. The measurement is taken off the datum line on the shoulder, not the belt. :confused:

:)
 
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Referring to headspace as anything to do with a case I believe is incorrect
because Headspace is a characteristic of a chamber (not a case, or ammunition).
Click to expand...

Yes, and no.

The headspace built into a proper chamber depends entirely upon the case being in spec as well. A perfectly good chamber within SAMMI spec, that should be safe to shoot, can still be unsafe with a case that is out of spec, wether the case was made that way, or ruined by improper trimming or sizing. (Human error)

Headspace is a relationship between brass and chamber. They both rely on each other.

A rifle with proper headspace built into a proper chamber is a static thing, and has nothing to do with case except the spec the case is supposed to be built to. It can be properly headspaced without a case, but after that it is totally dependant on the case to be safe.
 
Thanks for your responses to my questions. It seems that regardless of an “official” definition for headspace, reloaders use different definitions depending on the context, but in most cases the definition relates to how the cartridge fits in the chamber, and of course, headspace is measured differently depending on the shape of the cartridge case.

But my most important concern remains. To what extent do I need to worry about headspace for my reloading. My understanding is that I should not need to worry about headspace if I screw down my sizing die just right before I start resizing. But exactly how do I know if is “just right”? For example, on the Lee Breechlock press, the instructions say to screw down the sizing die an additional ¼ to ½ turn, except for carbide dies which you do not screw down any further after the die touches the shell holder. But how do I know if it should be ¼ turn, 1/3 turn, ½ turn, or something else? Can I tell simply by how well the cartridge fits in the chamber afterwards? Also, are the Lee collet neck sizing dies carbide dies and I should not screw the die in further? Thanks.

Greg
 
I told you in post #3.

You can avoid doing it by adjusting your sizing die until the bolt just closes with slight resistance on a sized case.
Click to expand...

Collet neck sizing dies are not carbide.
But if you are neck sizing only, none of the above 23 posts applies anyway, because they don't resize, or set back the shoulder which controls headspace.

rc
 
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