what exactly is headspace? what are the effects of having too much, or too little headspace? what can be done to correct either situation? i would really appreciate it if someone could define this for me in laymens terms. thanks
britt

Headspace is a measurement to a specific point on a case. when the measurement is correct, whether it be to a point on the casemouth, the shoulder, the case rim or belt the cartridge is held back against the bolt/breech. When it is closed the cartridge cannot move forward or rearward in the chamber. When detonated the only movement that can occur is for the case to expand and grip the walls of the chamber. Too much headspace can cause head separation and to little can cause hard or impossible chambering. In order to correct excessive headspace the barrel must be set back until that dimension is re-established. If there is to little head space then the chamber must be cut a little deeper. Jim

Simply put, headspace is the distance between what stops the cartridge from moving forward (be it the mouth, shoulder, belt or rim) and what stops it from moving backwards. The nominal diferance between Min and Max is about .005"
Not enough, and you won't be able to lock up the action.
To much and the cases will stretch excessivly, and with continued resizing and firing cycles, evedentully seperate at the head/web junction. Excess dosn't normaly cause a problem if your only using factory ammo.

1) The space in a gun for the cartridge case head [rim] with clearance was called "head space".



2) When rimless cartridges came out, the same term, head space, was used but the measurement was not about rim thickness with clearance, but from breech face to the shoulder with clearance.



3) The term gets further perverted when used to describe brass that has been fire formed in a chamber. Some say, "The brass now headspaces in that chamber."

Those explanations are correct but somewhat confusing to most shooters. Let me try it and please correct me if I am wrong as I look at headspace this way.

Headspace is the �slop� between the boltface and the cartridge head when the cartridge is chambered. This distance I believe should be at least 0.002� and not more than 0.006�. If you were to put a piece of shim stock between the boltface and the cartridge head and could close the bolt with slight resistance and your shim stock thickness was 0.0035�. Then you headspace is 0.0035� (acceptable). This cartridge when fired would or could move back 0.0035� into the boltface. I am saying that when the bolt is closed on a case, that case could move forward or backward a total of 0.0035�. Am I right? Is headspace the maximum distance from the boltface to the cartridge head when the bolt is closed on the case?

Here is an article on the topic

http://www.rifleshootermag.com/gunsmithing/headspace_0612/

My favorite headspace example is the 303 British:

SAAMI is .054" to .064" cartridges.

SAAMI spec of chambers is .064" to .071" chamber.



That .017" possible difference PLUS the stretchy Brit Enfield action [this is not just a gun culture legend, I calculated appreciable bolt body compression] means some serious stretching of the brass case wall possible.



Some complain 303 brass does not last long



--

A society that teaches evolution as fact will breed a generation of atheists that will destroy the society. It is Darwinian.

Head space is the distance between the case head and the breech face period. The measurement to
some spot on the neck is a datum line. Example: Toledo and Cleveland are 120 miles apart (headspace) but they are
measured from the prime meridian in England (datum line). As to the brass stretching, it is a little complex.
Thc case is driven forward by the primer (not the firing pin). It stays forward until the breech pressure reaches
about 40,000 psi. Then the case head stretches back. With a lower pressure cartridge "Headspace" will be
indicated by the primer projecting out of the seat.
Good Luck!

Headspace , the really short version :
The measurement between the case head and breech face when the cartridge is pushed fully forward in the chamber.

Travis F.

JBM and Travis F have it the right "practical" is easy answer but ONLY for brass in that rifle.

1) Imagine that you had a rifle whereby with factory ammo or new brass or a headspace gauge you could just close the bolt with .003" of shim stuck on the bolt face.

2) Now imagine that you machined .010" off the back of the locking lugs of that same rifle, you would now find that new factory ammo, new cases or a headspace guage would allow the bolt to be closed with a shim of .013" stuck on the bolt face.

3) With the same rifle with the lugs machined back the .010" if you now fired a factory round or a reload in the new brass...then rechambered the fired case with shim added to the bolt face then perhaps a shim as thin as .001" might cause difficulty in closing the bolt. You could now full length size the fired case and by adjustment of the full length dies your resized case might allow you to have .003" or .004" of shim on the bolt face and close the bolt on the resize case. Thus in this case the headspace would be OK in this rifle that had the locking lugs machined back with the resized cases (or the unresized fired cases). However, the rifle would have excessive case and this would be demonstrated by how much shim could be put on the bolt face while allowing the bolt to easily close on either a new case, factory ammo or a headspace guage.

Now say you took this same rifle before the locking lugs were machined back the .010" and you chambered a case that had been full length sized in a die that had been shortened or where a shell holder was used and that shellholder had been ground down. In this case you might be able to put .010" or .020" of shim on the bolt face and still close the bolt and this would be excessive headspace.

So the bottom line is that correct headspace for both safety and accuracy is governed by both the cartride case and rifle dimensions.

However in just about every case with an unaltered factory rifle or a rifle chambered by a competent gunsmith any headspace issue will usually relate to the brass and resizing. When someone on the forum says something like "my dies are set so I have about .003" headspace" then they are referring to the thickness of shim that can be placed between the bolt face while allowing a case to be chambered.

Mike

hey thanks for the answers, i understand now.
thanks,
britt

Of course it is.

I'm not arguing too much, or too little.
I'm not arguing benchrest shooters getting it perfect.
Too much is bad.
Too little is also bad.
Just right is good.
It isn't movement side to side.
It isn't movement up and down.
It's movment forward and back.
Something has to stop forward movement.
A rim.
A belt.
A shoulder.


Lighten up guys. I don't take myself too serious.

I watched geese migrate north the last two weeks.
And Sandhill cranes.
Applications for Colorado hunt in.
I'm walking four miles every day getting ready for Colorado.
Ice is out.
Boat is ready.
I'll be out on the water next week.

Dutch; Please explain how a cartridge can fit "perfectly" and have headspace?.
Also what cartridge has 2 in between the case head and the breech?.
Thank You!

Because headspace is not a measurement of movement, it a measure between two fixed points. The relative differences between the chamber dimensions and the cartridge case dimensions can cause conditions of "too much" or "too little" headspace.

Say a rifle chamber is 2.041" from the bolt face to the datum point on the shoulder of the chamber with the bolt fully closed. The headspace is 2.041".

Say a typical bottleneck cartridge that "headspaces" on the case shoulder measures 2.041" from the base to the datum point on the shoulder of the case. The cartridge fits the chamber perfectly but the headspace is still 2.041".

If the cartridge moved back and forth in the chamber that would be a condition of "excess headspace", although one mustn't get too strict about that word "excess". It is actually preferable for the case datum line to be about .001" to .002" shorter than the chamber in a hunting rifle rather than being a "perfect" fit as you want a teeny bit of clearance for ease of chambering.

Obviously a bit of confusion as the word "headspace" can be a noun or verb depending on it's context.

Headspace also has different meanings depending on whether it is used in a firearms related context or not.



The normal "headspace" on my '69 Barracuda was about 6 inches, that being the distance between my lap and the steering wheel.



I had to move my seat back to increase the distance to about 12" or more to allow both room for "expansion" and so my girlfriend's cranium would "headspace" properly.



Vita brevis, guys, lighten up.

My experiments show,it is the firing pin that drives the case forward instead of the primer as many believe.
Actions used were a Stevens Model 94 and an H&R single shot actions.

The cartridge case was a .303 British with a standard large rifle primer.

The actions were secured in an upright position and the primed case was placed on the breech face so the firing pin struck the center of the primer.The case was propelled about 10 feet into the air though the primer did not fire.

I then slid a 7/16ths nut,weighing 174 grs around the case to simulate a loaded round,the primer did not fire,the case was propelled about 3 feet upwards.I placed another nut on the case ans tried it again,the primer still did not fire.

The weight of the 2 nuts together was 358 grs.I tried to fire the primer a total of 7 times,the case with the nuts was propelled into the air each time though the primer never fired.I then chambered the case in my .303 and it fired ok.

This tells me that the firing pin shoves the case forward before the primer is crushed.

This experiment was carried out in such manner that no one was exposed to danger should the primer have fired.

WC

Wildcat Crazy,
Thanks for posting that.
Why didn't I think of that?

What Jim said. Thanks for the assist. Dutch.

Wildcat crazy: Your tests prove nothing because you didn't find out how far the case would fly if the
did primer fire.
A primer has enough force to push the shoulder back on light loads, that can't be due to the firing pin.
Good Luck!

Wildcat crazy: Your tests prove nothing because you didn't find out how far the case would fly if the
did primer fire.
A primer has enough force to push the shoulder back on light loads, that can't be due to the firing pin.
Good Luck!

Hatcher's Notebook has an interesting discussion of that. They found amongst other things that vigorous operation of the bolt could set back the shoulder quite a bit. BTW the the technical headspace of the 30-06 involves a point that doesn't exist on the case.It is the intersection of the line of the body and the line of the shoulder.

If the primer will push the shoulder back with a reduced charge then it should push the shoulder back by firing the primer without powder or a bullet.

I have an H&R Handi Rifle chambered for a rimmed wildcat,I formed a rimless round so the extracter would not interfere.
The head of the case was .002 below the end of the barrel before firing with the primer.After firing 11 large rifle
primers in the case without sizing the case it still measured .002 below the end of the barrel.

I leave about 1" headspace in the jars when I'm canning venison. 75 min. at 11# for pints @ 3000 ft. elevation, 90 min. for quarts. One teaspoon of salt per quart, for flavor. YMMV.
Jay, Idaho

mete; Right on
If the shoulder isn't pushed back why will a case stretch in a chamber with very little head space?.
.Although reading primers is a little like reading tea leaves, a "riveted" primer (flat but wider than the seat)
can only occur with headspace allowing the primer to bulge out before the case comes back.
Sometimes you can get this with a minimum headspaced chamber, so the shoulder must have been back.
Things aren't simple during the first few milliseconds.
Good Luck!

I have done some machining and drilling and fitting; strictly amateur stuff. I would like to see somebody fit a 2.041 anything into a 2.041 hole. The thing has to be a tad bit smaller, hence the term �space� in headspace, the term for how much a cartridge can move forward or backward and still be safe to fire.

Wildcat Crazy; The end of the case is not open when the primer fires. Crimp a bullet into an empty case
and repeat ypur experiment. Have a strong solid cleaning rod handy to remove the stuck bullet.
Good Luck!

Headspace is just as written. The space between the case head and breech of the rifle. Headspace gages are built according to datum points in the chamber and are only used to measure the theoretical amount in a perfect world. As others have posted here different ammo can produce different amounts of space between the case head and breech "headspace". The distance from the breech face and datum point hasen't changed, but the headspace with different length cases does.

gunmaker
http://users.elknet.net/chico

irv,

I took your advice and loaded 150 gr.bullets however I switched to magnum primers.

I loaded and fired the case 10 times,the shoulder did not set back.The measurement remained .002.

I did not have to resize as the case did not show any expansion.The case grips the bullet as tightly after 10 firings as it did the first time.The bullet only engraved
into the riflings 1/4 inch.I have a steel rod .291 dia.that I use to remove stuck .30 cal bullets.

I believe most of the "shoulder setback"is caused by radial expansion and neck sizing only.

A 7.62x39mm will not chamber in my wildcat but protrudes about .010 from the chamber.A fired 7.62x39mm will chamber
with about .005 to spare.The factory 7.62x39mm was fired in a sks with a sloppy chamber.Due to radial expansion the shoulder length was short by .015 after firing,full length resizing brings the shoulder back to the proper location.

Upon discovering the fired 7.62x39mm would chamber in my cat,I measured the depth it sat in the chamber,it was .005.
I loaded the 7.62x39mm case with 3grs.of Green Dot and a 100
gr.cast bullet sized .313 and fired it ,the shoulder did not set back.

WC

wildcatcrazy: One thing I will admit; The more I learn about these things the less I know.
Light (used to be called "gallery") loads may develop headspace. I have seen this, and all the old
reloading books warned about it. I have a problem picturing the firing pin setting the shoulder back.
Now your experiment gives me a lot more to think about. In particular the neck staying tight.
There are a couple of questions (for now) that come to mind; How much forming has the case neck/shoulder
been through?. Perhaps if it were annealed it would have a different behaviour. The other difference could be
that the primer has a very rapid pressure rise (impulse) perhaps the neck would respond differently???.
Anyway thanks for the input, I'll be playing around with this this summer. Once you begin to wonder
"what is really going on", you are cursed.
Take Care!

I had to go out of town on the afternoon of the 9th and just returned home this evening.I sat and held my mother's hand from Saturday until she passed away Tuesday evening,not a pleasant experience.

Possibly,I can get back to experimenting tomorrow.

WC

My condolences.
Was where you are, in 94 with my mother.

Wildcat crazy; Sorry to hear about your mother. The thing to now is remember the good stuff
about her, and pass it on.
Take Care!

Thanks fellows,she was just shy of 80 and had suffered badly from cancer for a couple of months so it is for the best though it was a difficult time.

I had some interesting results from my tests ,today.

First,I made a gauge so I could measure from the center of the shoulder to the base,on both rimmed and rimless cases.As I mentioned in an earlier post my wildcat is based on a rimmed case{.303 Br. shortened}.

For the tests ,I used one case formed from .303 Br. and two
cases formed from .35 Rem. All three cases measured 2.247 in the gauge.

I annealed all three cases on the neck and shoulder to dead soft.I primed case no.1{.35 Rem.} with a magnun primer and fired it.It did expand in the neck and shoulder.when guaged it measured 2.243,it shortened by .004.

Case no.2(.35 Rem.}was loaded with a large rifle primer,3
grs. Green Dot,and a 110gr.RN bullet,it shortened by .005.
I neck sized and reloaded it.On the second firing it shortened an additional .006 for a total of .011.The case was neck sized and fired two more times without shortening more.

Case no.3 provided the big surprize.The headspace on it was.002,when it was loaded and fired with the same load as case no.2 it shortened by .003 though the headspace remained .002.On the second firing it shortened another .004
for a total of .007 the headspace remained unchanged at .002.

The shortening of the shoulder length on case no. 3 seems to confirm my conclusion that radial expansion coupled with neck sizing is the real culprit in cases shortening with reduced loads.

Tomorrow I'll anneal another case{.35 Rem.}and use an inert primer to see if the firing pin causes any of the set back on the rimless cases.

WC