Headspacing

[shredder4286]

gentelmen- i'm tryin to understand headspacing an how it applies to reloading. correct me if i'm wrong, but headspace is the distance from where the head of the casing meets the breechface, to the point in which the shoulders of the case meet the chamber of the barrel.
the thing i'm also wondering about; for example: if you fire a .30-06 round through say a remington model 700, is it best to reload those casings for use in the same rifle only? or can you reload those rounds and fire them through a different rifle of the same caliber? thanks in advance

[William T. Watts]

I use Wilson Cartridge Case gages to set my resizing die, if I am loading for two or more rifles of the same caliber I drop the fired cases into the gage (has steps in the gage to show minimum and max heaspace) to determine which rifle has the least headspace. The rifle that has the least headspace is where the sizing die is set - .001, if the resized cases function thru the least headspace chamber they will be fine for the second rifle. Using the Wilson Cartridge case gage you can set your sizing die precisely so your finished ammo will function thru multiple chambers, follow the instructions and you will be fine. Hope this helps! William

[mehavey]

...headspace is the distance from where the head of the casing meets the breechface, to the point in which the shoulders of the case meet the chamber of the barrel.

That's roughly correct. "Headspace" is nothing more than the extra room that a cartridge has to rattle back & forth in the chamber when the bolt is closed. Every rifle's chamber dimensions are slightly different, but all are within a +/- spec of a few thousandths to the SAAMI standard.

For the 30-06, the chamber must measure

- At least 2.0487" long (must "GO" Gauge)
- Preferably less than 2.0547" long (factory standard: "NO-GO" Gauge)
- ...and absolutely less than 2.0587" (Maximum safe "FIELD" Gauge

All commercial ammo is sized approx to/under the GO dimension to fit in all rifle chambers for that cartridge (even "tight" chambers having minimum dimensions). First firing will stretch the case to fill the chamber. Upon extraction (theoretically), the case will now have the actual headspace dimensions of that specific rifle. If left at that dimension (and the rifle had long headspace) that case might not fit other rifles having smaller chambers -- even though those other chambers were within "spec".

The re-sizing die solves that problem as it swages the case back down to (as much as) minimum headspace again so that it will fill all rifles.... not just the one it was originally fired in.

[wncchester]

"i'm tryin to understand headspacing an how it applies to reloading."

Let me simplify this and explain "how it applies to reloading."

First, forget how it's measured. If a case is rimmed, rimless, belted doesn't matter, where it's measured and how it's measured matters not a bit to us. What matters, and all that matters, is how well our finished cartridges fits a chamber.

There must be enough room in the chamber to allow the cartridge to fully enter and the action to close on it. If there's not enough headspace we can't close the action, it's that simple. On the other hand, if there's too much headspace the cartridge will be a rattle fit. Clearly, neither is good. But, it really doesn't matter what the actual chamber headspace is to a reloader, we can size the cases to fit snugly.

Your resizing target can be to return to SAAMI (industry) standards and that's what most "full length" resizing does. If we do that, we simply remake cartridges that will fit and function in any rig ever made for that cartridge. That's good, sorta, but it's not real good for reloaders because it deprives us of a custom fit and that's one of the major advantages of handloading!

For reloaders, knowing the +/- dimensions of headspace for a cartridge or knowing how it's measured means nothing, that's for gunsmiths to worry about. Using chamber gages (Wilson and others) only insures we have indeed returned to a universal - not best - size. But what we should really want to do is make ammo that perfectly fits the chamber we have. IMHO.

Rimmed straight wall cases fit or there is nothing we can do to change it.
Rimless straight wall cases fit at the case mouth, we can foul that up by excessive crimping but if we use taper crimps - which is all most dies for autoloaders do - it's not really a problem. So, most problems occur with bottle neck cartridges.

FL sizing a bottle neck case happens without measuring anything when we simply jam the case as far into a full length sizer die as we can while using a standard shell holder. Done that way we squeeze down the external diameter AND push the shoulder back to the standard, okay? Question is, do we really wish to do that? I don't.

I prefer to size my reloads so they fit MY gun, not everyone elses. That can be done by neck sizing, without touching the case body, so it continues to fit my chamber snugly. Or, it can be done by what's sometimes called "partial FL sizing" but the term "partial resizing" doesn't have any solid meaning, other than the case sorta got pushed into a die. I want to precisely custom resize my cases. Custom sizing means it's made to perfectly fit MY chamber, with little slack, or excess "headspace." Done properly, even an old, worn rifle with "excess" headspace will have new ammo that fits as tight and safely as any other rifle.

In effect, custom resizing simply requires setting the shoulder (and that is the only important headspace dimension) of any bottle neck cartridge back only to the point it was after firing. The fired case has fully expanded and shrunk back from the full chamber length already so setting the shoulder back further just increases the headspace/sloppy fit! Custom resizing a shoulder back to the fired position insures easy chambering and is a good fit - which is all that headspace is really about - and limits case stretching to almost nothing.

Get a RCBS Precision Case Mic, or the Sinclair or Hornady LnL case measureing tool for use on a precision caliper, or the Innovative Technologies case measuring tool and use it to find where your fired shoulders are. Then adjust your FL sizer to return the sized shoulders to that point and headspace won't be a problem.

[Brian Pfleuger]

Speaking in terms of mainly rifles:

In addition to what the gentlemen above have said, one of the problems with repeatedly full length resizing a case is that the headspace is repeatedly reset to "factory spec" which is not correct for most any individual firearm. Every time such a cartridge is sized and fired, there is a small amount of stretching in the critical head region. Eventually, if the process is repeated without noticing the warning signs, the case will rupture/separate in the head region.

From the research that I have done and questions asked, I believe that the best way to prolong the life of a case, prevent danger to the shooter and achieve optimal accuracy is to first fireform all new cases to the individual gun by using a sub-20,000psi charge of either a fast pistol powder, like Unique, or by using IMR Trail Boss. After the case is formed to the chamber, a Lee collet neck sizing die can be used on the neck and then a Redding body die can be used to resize the body and "bump" the shoulder (if desired) without completely restarting at "factory spec". Such an approach both minimizes stretching in the head region and also enhances accuracy.

In both my Encore and Ruger M77, I have found no need of resizing the body through at least 3 full power reloadings of the same case, so I use the Lee collet die almost exclusively. YMMV.

[Loader9]

Here's the definition of headspace from Fulton Armory:
http://www.fulton-armory.com/headspace.htm

Headspace is different from a rimmed cartridge, rimless, belted, etc. as in how/where it is measured. But to more directly answer the question, a round fired in a Remington 700 can be full length resized, loaded, and shot in another brand rifle with zero issues. The full length resizing brings the brass back to specs to be used in any rifle of that chambering.

[shredder4286]

Get a RCBS Precision Case Mic,(etc) measuring tool and use it to find where your fired shoulders are. Then adjust your FL sizer to return the sized shoulders to that point and headspace won't be a problem.

so, once you fire the new shell for the first time- that's when you measure w/ a case mic (or any of those you listed) and find where your fired shoulders are? or am i confused...

BTW, thank you all so much for the info, it's greatly appreciated

[wncchester]

"so, once you fire the new shell for the first time- that's when you measure w/ a case mic (or any of those you listed) and find where your fired shoulders are?"

You are not confused.

There is so much info on "head space" floating around that is, of itself, good enough but most of it gets so technically oriented about how and where to measure it that the infomation the poor reloader who needs to know how to deal with it usually does get confused. That need not be.

I actually hate to write long posts but it's too hot outside so I have time on my hands. I just did my last (I hope) edit so perhaps you might want to re-read it. ?

And there is no advantage to "fire forming" any normal cases with reduced charges to get them to fit, best fit occurs quite well and quickly with normal loads.


Good luck!

[shredder4286]

You are not confused

so, after the 1st fire, you measure, annotate the dimension of the neck diameter, but at that time, there's no resizing required. henceforth, the 2nd and 3rd time that shell is fired, and the dimension exceeds the width that it measured after the 1st firing, it needs to be resized to the width that you recorded. simply put, the 1st firing puts the neck at the optimal size for the rifle you fired it through

[mehavey]

An addemdum to the above....

Bolt guns are very forgiving if/when you fire & reload in that particular rifle. In fact you can leave off full-length resizing altogether and just size the neck down from reload-to-reload to ensure the bullets fit tightly each time. The bolt's camming action will ensure solid lock-up upon chambering. **

Autoloaders are not (repeat, NOT) so forgiving. You must either

- Full-length each time... and resign yourself to discarding the cases early so as not to have an eventual stretch-induced head separation. (Badd juju)

...or...

- Get a cartridge headspace gauge (RCBS and/or Hornady). Then you measure the headspace dimension on the fired case(s) and adjust the sizing die's lock-ring to knock the shoulder back only ~0.002"(+/-). This case will now chamber/lock-up reliably and not overly stretch on firing -- doubling case life or more. But `ya gotta know what yer doin'.

.

.

** Even when only neck-sizing (old method: back off the FL resizer a turn or so to where you don't engage the case body), you will still have gradual creep to where the case gets harder to cam into lock-up over time. Then you knock the shoulder back a bit (until it again chambers with "bare feel") and start the sequence of neck-sizing-only again.

[shredder4286]

again, guys thank you all so much for the info. i'm not gonna be back in the states for another 9 months, so until then i can't put this knowledge into action. i already have most of the equipment needed to start. for now, i'm just tryin to gain as much info as i can so when i get back, i can start with a little more knowledge than i would've otherwise

[wncchester]

"so, after the 1st fire, you measure, annotate the dimension of the neck diameter, but at that time,... "

All right, you ARE a bit confused! Forget the references you've seen about the headspace "datum line", which IS a diameter at about mid-shoulder, because none of that matters to us. I wasn't refering to the neck diameter at all, necks have nothing to do with headspace. Any common sizer die (FL or neck) will take care of the neck diameter as part of it's normal function, we need do nothing.

All you really need to know is that effective bottle neck "headspace" applies to the shoulder location as it's measured from the head. The various gages I listed will take that measurement very well, and from that length you can adjust the FL die up-down until the sized shoulder matches the fired location.

Read it all again with these thoughts in mind.

[TXGunNut]

So, the tell-tale lines hinting at head separation show up after the first firing of new, factory brass and after 3-4 reloadings (FL sizing) the black stuff starts coming thru the cracks. Do I neck resize or contact the warranty center? New gun, BTW.

[mehavey]

Get a gunsmith to measure two things:

- What is the headspace dimension of one of your fired cases
- What is the headspace dimension of one of your fully-resized cases.

If the dimesions of the fired case are within spec (i.e., the chamber is within spec), warranty center work cannot help. (But if your are already getting annular rings on new/1st-firing, the fired case is probably gonna show excesive headspace right off the bat. But measure first.)

If fired case/chamber is in spec, but the difference between the fired/full-length-resized case still exceeds 0.006"-0.008"....

(1) Autoloader: Your only option is to get a headspace gauge of your own and adjust the sizing lockring.... or commit to throwing cases away early

(2) And if this is a bolt gun: Just neck size from now on

[rg1]

I load for 5 different 30-06's. Some of my 30-06 loads are for my bolt action only just because of the powder I use for it. All my other loads are for firing in all 5 of the rifles. 3 M1 Garands, Remington 742 semi-auto, and a Remington 700 bolt action. I want all my loaded 30-06 to chamber in all the rifles "if necessary" so I size my brass to fit the tightest chamber, the 700 Rem bolt action. It's chamber is about .004 past zero while the 742 and Garands is on the long side of specs or about .008" past zero. I size all the brass to push the shoulder back to about .002-.004" above zero. I know this is not the perfect system but I don't push the limits on pressure and inspect all fired cases very closely for signs of stretching etc. I also don't plan to fire each case more than a few times each. I also want my loads to chamber and be safe in your rifle should the need arise. I have the same issue with .223/5.56 rifles and load for more than one rifle and different types. Now for my one of a kind calibers such as 25-06 or .300 Weatherby I tend to size brass specifically for that one rifle. A RCBS Precision Mic or Hornady's Headspace Gauge Set will help you adjust your sizing dies to push the shoulders back a measured amount and are highly recommended. Also, careful case inspection is a good safety practice. Check out these two sites:
http://www.realguns.com/archives/035.htm
http://www.inlandshooters.net/index.php?contentid=99

[FrankenMauser]

I agree, that in general, reloaders don't have to worry about head space.

But... the datum line is only "about mid-shoulder" on most '06-based cartridges. (Which happens to the the point on the shoulder at which the standard dimension chamber has a diameter of 0.375")
Most other cartridges have the datum line located at or very near the neck/shoulder or shoulder/body junction. And rimmed and belted cartridges, of course, don't use a datum line measurement for head space.

[shredder4286]

All you really need to know is that effective bottle neck "headspace" applies to the shoulder location as it's measured from the head. The various gages I listed will take that measurement very well, and from that length you can adjust the FL die up-down until the sized shoulder matches the fired location.

ok, so i had the right idea, i was just talking about measuring the wrong part of the casing. the gage you suggested was for measuring the distance from the head to the shoulders, right? so after the 1st fire, you measure that distance, and annotate it. that's your fired shoulder size. after the 1st fire, that's where you want to resize the casing to. is this correct?

[dmazur]

... so after the 1st fire, you measure that distance, and annotate it. that's your fired shoulder size. after the 1st fire, that's where you want to resize the casing to. is this correct?

And previously, by mehavey -

- Get a cartridge headspace gauge (RCBS and/or Hornady). Then you measure the headspace dimension on the fired case(s) and adjust the sizing die's lock-ring to knock the shoulder back only ~0.002"(+/-). This case will now chamber/lock-up reliably and not overly stretch on firing -- doubling case life or more. But `ya gotta know what yer doin'.

There's one school of thought which says a slight crush fit is fine. After all, a bolt-action has incredible camming power. Another school says to adjust the die for 0.001" to 0.002" smaller than the measured fired case length. That way, you don't have a round that won't chamber when you want it to on a hunting trip.

As long as you aren't unnecessarily resizing to SAAMI minimum, you aren't over-working the brass near the head. This means longer case life (more reloadings) and less risk of case head separations.

There are stories of some guy who didn't understand headspace and was experiencing case head separations every 15th round or so during a match. An experienced shooter checked his ammo and found it was undersized by something like 0.015" or more. Apparently, that is more stretch than brass can handle...

Another thing that can occur is actual failure to fire. I believe this is related to how well your extractor holds the case, but it is possible for the firing pin to drive the case forward until the shoulder touches and not fire the primer.

Excessive headspace is something to understand first, and then set up your equipment to avoid creating it. For a variety of reasons.

[Jim243]

I should be the last person on earth to explain "headspace". Maybe unclenick will pipe in and give a better explaination.

But here goes.

To understand headspace you first need to understand what happens inside your chamber when a cartrage is fired. There is a misconception that the case holds the chemical reaction that happens when the primer sets off the gun powder. This is not true, your chamber is what keeps you safe when the cartrage goes off. Brass is harder than pure copper, but harden steel is what is needed to contain the explosion. When the primer is set off it ignites the gun powder and is blown out of the case and slamed against the bolt face. The rest of the case follows a split second later and reseats the primer back into the case. Excessive headspace will make the primer look like it does in an overcharge, even though the charge may not be an overcharge. That is why checking the primer only is not a good indication of a overcharge, because it may be a headspace issure.

When the gun powder is ignited, there is an extreem amount of heat and pressure generated that softens the brass case, some say it makes the brass flow. This pressure and heat is what forms the case to your chamber and is called "fire forming" the case. The metal in the case (brass) will bounce back (not completely) to it's original shape, or you would never be able to get the case out of the chamber. This process places a strain on the brass case, but specificaly in two areas, the neck and the web of the case (that area closest to the head of the case). Repeated firings and use of the case will eventually stress the case to the point of failure, spliting the neck or seperation of the head from the rest of the body of the case. And in some cases a split down the whole body of the case, but usually the neck will split or the head will seperate first.

Now we can get to headspace. For necked rifle cases you are correct it is measured from the mid shoulder (datum) to the bolt face, for belted magnums it is from the belt and for straight wall cartrages it is from the case mouth of the case.

It is believed by many and provened by benchrest shooters that fire formed cases give better accuracy. But they should only be used in the rifle that they were fire formed in. They will provide chambering issues and headspace problems in rifles that they were not fire formed in.

Since the neck and case will stretch and expand, special attention and handleing is needed to bring them back to a shootable condition. The first is neck sizing with a collet die for the neck and bumping the sholder back, the second is trimming to proper length and often they will be annealed (a heat process to soften the neck) to make them last longer.(the more often you use a case, the harder the metal gets)

Since I don't shoot benchrest matches (for money, or anything else) I do not fireform my cases and ALWAYS full lenght size my cases.(even thou I have collet dies) And if there is a headspace issue it would be because I pushed the shoulder on my case too far down. (I do test my die settings before making a run to insure that the empty case chambers correctly before making a run of ammo that I would have to throw away.)

I hope this helps.
Jim

[wncchester]

"the gage you suggested was for measuring the distance from the head to the shoulders, right? so after the 1st fire, you measure that distance, and annotate it. that's your fired shoulder size. after the 1st fire, that's where you want to resize the casing to. is this correct?"

Now you've got it. Again, it matters not what the case datam/diameter line is nor where it's measured nor if it's rimmed or belted, size them all as rimless and make them fit your chamber.

IF you measure and duplicate the fired shoulder location in your longest fired case (they WILL vary a couple thou, nothing you can do about that) then you won't get a "crush fit", you will have the same fit as after it was fired and that's plenty loose. (They will also vary a couple thou after being sized, so use the longer ones as your reference for adjusting the sizer.)

[wncchester]

"So, the tell-tale lines hinting at head separation show up after the first firing of new, factory brass and after 3-4 reloadings (FL sizing) the black stuff starts coming thru the cracks. Do I neck resize or contact the warranty center? New gun, BTW."

Tex, I can't imagine a new rig having enough headspace/chamber slack to give signs of an impending seperation from the initial firing but it's possible. Asking the warranty people about it would be a very good precaution. Whatever, getting/using a case headspace gage and resizing as described above will, or should, fix it.

Otherwise, how quickly anyone starts seeing head cracks & leaks depends on how much they over resize, usually simply by jamming cases fully into the sizer each time and setting the shoulder back too far so they get maximum stretching with each firing.

The main advantage new loaders have over us old dudes is all the measuring tools that can tell you what's going on. Only a few reloaders even had micrometers in the 60s and virtually no one had a precision caliper! We learned by experimentation, most of us lived. (And, for sure, no book tried to tell us what magic OAL to use for specific bullets! )

[Gunplummer]

There are so many variables involved in headspace that it should not even be discussed on a forum, especially to some one totally unfamiliar with the mechanics of it. It is a fact that older U.S. military rifles do not headspace the same as civilian counterparts. The chamber specs are different and the ammunition specs are different. A lot of imported military guns do not use the same specs either. Many a 98 Mauser will fail the no-go gauge check that is called off the shoulder and be perfectly safe to shoot. If you are cheap and pick up junk brass, sort it out and use the biggest brass. Manufacturers specs vary. Mic the head of unfired brass until you find the company that stays on the high with their brass. Out of the "big 3", I have found Remington and Federal to be the largest made brass. Winchester is so small it looks dangerous after one firing in an older Military rifle. I am not going to get the book out, but if I remember correctly, the body diameters on ammo have a .010 tolerance. That is a heck of a lot when you add all the other tolerances in with it. If you sort your brass and stay with the biggest diameter stuff, it will solve a lot of problems for you. Unfortunately, as others stated, the reloading game has to be learned. A lot of the tricks you pick up are not in the book.

[mehavey]

There are so many variables involved in headspace that it should not even be discussed on a forum, especially to some one totally unfamiliar with the mechanics of it.

I agree with gunplummer.... except where else does one start learning? Old Fogeys are best, and boy do we have them here !

That said, and while old milsurplus weapons and ammo may have slightly different reference specs today, the cartridge must fit the chamber to be (A) safe, (B) accurate, and (C) long-lived for reloading purposes. That means headspace “matters”.

If a rifle (of whatever vintage) fails a headspace check, it pays to know what 'GO', 'NO-GO', and 'FIELD' really means.

GO and NO-GO are factory references. The chamber has to be manufactured big enough so that the 'GO' gauge will fit in within it. But it shouldn't be so big that 'NO-GO' will slip in as well. If buying a gun from the factory, from a dealer, from the guy next door, it should pass these two checks.

'FIELD' is the biggest gauge of all, and is the last-ditch safety measure. If a rifle that you already own/shoot -- no matter what vintage or collector status -- has a chamber so big that it will close on a 'FIELD' gauge, it is UNSAFE to shoot. Period. (Translation: If Granddad's 98 Mauser fails the FIELD gauge for headspace, it's toast until you find a new bolt.)

Conversely, If the bolt will not close on the FIELD gauge, the gun passes the headspace test for military/"field" use as the chamber is small enough to shoot new ammunition in it -- once. After that the reloader must neck-size only (or be able to measure/adjust/limit his sizer for only 0.002" shoulder set back from as-fired condition. Otherwise, full-length resizing is guaranteed to cause head separation in short order as the case can only take a few stretch cycles this large.

[wncchester]

"It is a fact that older U.S. military rifles do not headspace the same as civilian counterparts. The chamber specs are different and the ammunition specs are different."

"Otherwise, full-length resizing is guaranteed to cause head separation in short order as the case can only take a few stretch cycles this large."

So...the solution is to size the cases so they fit. End of story.

[TXGunNut]

Hate to disagree with someone more knowledgeable on the subject than I but I would like to know more about headspace issues and folks like you can teach me a lot about it, Gunplummer. I'd rather hear your thoughts on the subject over a cup of coffee or at a workbench but this is what we have.
Nice post, Jim243. It helps.
Good folks @ Winchester/Browning said send it back, wncchester. Wondering if I should buy a set of gauges for the next rifle or just take it by a gunsmith to check it out before I invest a lot of time in load development. This is a hunting rifle and I hunt with new cases but I like to play and I'd rather buy bullets, powders and primers than cases. I also suspect the headspace issue is behind the erratic accuracy issues.
I think you've answered OP's question but as Gunplummer implied this is a complex issue, or so it seems to me.