Can someone point me to a site that explains Checking Headspace in a way that I can understand? I need a site with really big crayons cause it just doesn't seem to sink in to my hard head.

First, do you actually understand what "headspace" is? I'm not questioning your intelligence, it's just that so many shooters don't really understand. The fact that you seem to want to "check headspace" without outlining any problems with your gun that indicate a headspace issue implies to me that you've somehow come by the notion that "headspace" is something that "needs checking".

If you'll describe why your interested in "checking headspace", then maybe some of us can help you with whatever issue you're dealing with.

I don't mean to sound condescending or unfriendly, it's just that there's a great deal of misunderstanding about the term "headspace", which is the relationship of the breech face and the opposite bearing surface of the chamber to whatever portion of the brass case (rim, belt, shoulder, mouth) that it seats against and the dimensions of the brass case itself.

Let's hear more about your gun, Ron.

No, I'm not trying to check headspace on any of my guns, I am just trying to grasp the entire concept. I read here and there about people checking or should I say trying to check headspace and have seen quite a bit of disagreements about how to check it. I am quite adept at repairing anything but for some reason I just cannot get this issue straight in my thinking.

Headspace is a standard by which each cartridge must adhere to. It is a measurement to which the dimensions must be held to for safety reasons, and as stated before, it varies by whether it is rimmed, rimless, belted, ect. Some may have differing ways of establishing or checking headspace, but the "standard" way is with go, no-go, field gauges. Using cartridge brass should not be used since the dimensions can vary with brands. Die makers use SAAMI dimensions to make reloading dies, unless someone makes a wildcat.

There are many definitions, scenarios, conditions, but using gauges is the proper way to go.

By the way, I liked your other avitar better.

ronsguns



The term "headspace" comes from the old days when the majority of cartridge cases were rimmed. It signified the "space" occupied by the "head" or rim of the cartridge.



Today we have rimmed, rimless, semi-rimmed, and belted cases but we still use the term "headspace". As Stonecreek and Wayne said, it now denotes the distance between the bolt or breechblock and the point in the chamber that stops the forward movement of the cartridge when it is being seated. On a rimmed case it is the front of the rim, on a rimless case it is a point on the shoulder, on a belted case it is the forward end of the belt. It becomes very muddy when we get to semi-rimmed and some handgun cartridges and I don't want to even try to clear that mess up.

Okay, Ron, I like your attitude. Here goes:

First, why is headspace important?

Well, if there is "too little" of it (headspace too short), the cartridge will not chamber and allow the bolt to close into battery position because the base-to-(rim, belt, or shoulder) dimension of the case is longer than that of the chamber. In other words, the rim of the rimmed case is thicker than the chamber recess it is designed to fit in, or, most commonly with bottleneck cartridges, the base-to-shoulder dimension of the case is longer than that of the chamber. "Too little" headspace simply won't allow your gun to chamber the cartridge. An extreme way of looking at it would be the example of attempting to chamber a .30-06 cartridge in a .308 Winchester chamber, which would create an instance of extremely inadequate headspace.

On the other hand, if headspace is "too long", then other problems arise. Reversing the example above, if you attempted to chamber a .308 cartridge in a .30-06 chamber, then you would have a case of extemely excessive headspace. If the action were the "push feed" type, then the chambered cartridge might go so far into the oversized chamber that it would not even fire, due to not being held firmly enough against the firing pin (in a rimless bottlneck cartridge, it is the contact of the cartridge shoulder against the forward end of the chamber that holds the cartridge in its rearward-most position-- disregarding for the moment whatever effect the extractor hook might have.) If the .308 did fire in the .30-06 chamber, then two things would occur.

First, the case walls would grip the chamber tightly and the increasing gas pressure would shove the head of the case rearward until it was stopped by the bolt face. This would result in considerable stretching (and thinning) of the case walls near the rear of the case (you see some of this in almost any fired cartridge/chamber combination -- the slight bulge in front of the rim that many people call the "pressure ring". Except that with such a gross misfit as a .308 in an '06 chamber, the pressure ring would represent excessive brass stretching and case wall thinning -- in fact the case wall could get so thin on the first firing that it could either separate upon firing or separate upon a second reloading an firing.

Second, on the other end of the case, the shoulder would be expanded by the gas pressure until it reached the corresponding shoulder walls of the chamber, resulting in a very odd looking case that was all body and no neck. Actually, the brass would probably not be elastic enough to hold together, so it would split longitudinally at the neck as it tried to fill the oversized (excessive headspace) chamber.

Okay, so that's an extreme example. But what most people are concerned about is whether the "headspace" of their rifle is suitable enough that it doesn't result in excessive case stretching with ammunition designed for it. This is where things get trickier, because, in my opinion, almost ALL rifles chambers are reamed larger than they should be and almost all ammunition is speced smaller than it should be. Large chambers and small ammunition make for easy, sure chambering, and that results in no complaints to the manufacturers about "ammo that won't fit my gun". Of course, there has to be SOME difference in the length of the chamber (longer) and the length of the ammunition (shorter), or it wouldn't go in the gun. The question that arises is "how much is too much". Well, if you only intend to fire a cartridge in a gun once and not reload it, then you can get by with headspace that is rather excessive, so long as it does not result in the gun misfiring due to the firing pin not adequately striking the primer. Put it this way: If the firing pin will strike the primer with enough force to ignite it, then the case will stretch enough without losing its structural integrity to fully fill the chamber. Hence, there's hardly such thing as "dangerously excessive" headspace in a modern firearm in good condition.

Now, if you are a reloader (and what are you doing here if you're not?) you are concerned about the re-use of the fired brass. If there is an excessive headspace condition (whether caused by the chamber being signicantly longer than the industry standard, or by the ammunition being considerably shorter than the industry standard -- it's all relative of course) then your fired brass may be unsuitable for reloading. There are a number of "tricks" to customize your unfired brass to your overly-long chamber prior to firing it, but that is the subject of reloading methods, and not of "headspace" per se.

Speaking of reloading, if you have a full length sizing die and you simply screw it down against the shell holder head for maximum sizing, then you are likely creating more headspace than is desirable. Remember -- headspace is the relationship between the chamber "size" and the cartridge "size" (length), so it doesn't matter whether your chamber is longer than standard or your ammunition is shorter than standard, either amounts to creating excessive headspace (which primarily results is the case head separating from the case body at the pressure ring in only a few firings -- and this separation can be nasty, resulting in gas leakage into the action, blown extractors, and pieces of brass blown back into the shooter's eye in the more extreme instances).

Remember: There ain't no such thing as excessive headspace in a gun alone. It takes two to tango, so you have to have ammunition that is also too short for the chamber in order to have "excessive headspace". Since I'm a dedicated reloader, if I came across a gun I liked (chambered for a bottleneck cartridge) and its chamber's headspace dimension were such that it was inappropriate to use factory ammunition in it, this would mean little to me as I would simply load my ammunition (using one of a number of methods) so that it properly "headspaced" in my chamber.

Hope this helps. I tried to use the largest crayons I had. Feel free to ask for clarifications.

Guys
Thanks for the replies, I am going to keep reading them until I get it through the gray matter (my wife calls it rocks) but then what does she know! Stone thanks for taking the extra time to go into such length and detail and I am sure I will have more questions sooner or later.
Thanks again

JAL

The "field" gauge is not normally used in sporting rifle applications. You're right that it is a military gauge. When a battle rifle accepts the field gauge it is withdrawn from service and either destroyed, stripped for parts or returned to the armory for repair. The U.S. 30 M1 Rifle field gauge was .008" over the minimum gauge. During WWII the Germans were much more liberal and their field gauges were as much as .012" over minimum.

Look at the available "Field" gauges, and you will find that they are almost exculisivly for military cartridges.
Even the military reserves there use for those times when the fighting/repair load is so heavy that they don't have the time/parts to make proper repairs. Read that as to long to meet spec, but not yet long enough to scrap out (and that's what the military does to rifles that close on a field gauge). Think about it, the chamber dosn't move forward from firing, but the bolt/receiver lugs wear and pound back from use. Once that amount of wear is reached, rebuilding is no longer justified.

I believe I understand headspace somewhat, now I have a followup question: How is headspace set/adjusted? for example during a barrel change or if it is found to be excessive.

Well the amatuer way is to screw the barrel in on a live
factory cartridge until it stops, then back off a bit and
your there. Don't try this at home, it takes years of
practise. But that gives you the theory so to speak.
I hope the others here will state the correct way.
John L.

It's set with a reamer and a lathe (on normal guns). To short you run the reamer in deeper, to long you turn off some of the barrel seating surface.
Think of it this way, you want to drill a hole exactly .5000 deep in the end of a shaft. If your not deep enough (.4950) you would run the drill in again, if your to deep (.5050) you would face off the end of the shaft by the same amount (.0050).
The smiths I know shoot for zero to .001 headspace (just closing on a GO gauge) , and can tell from the measurments on the lathe where it will be at when screwed into the receiver (measurments of the receiver seating surface to bolt face dimention - allowance for stretch when tightening = amount of GO gauge protruding from the chamber).
"Bubba" smiths use a B&D drill, and hope that the customer dosn't notice/reload.

ronsguns

On some bolt rifles, such as the Savage, the headspace can be adjusted using the nut that holds the barrel on the action. But you still need a gauge to do it right, and I emphasise "right". The old Browning MGs were adjusted the same way. Isn't that right guys? I was in artillery and we didn't have headspace problems.

Ray

In it's simlest essence headspace is merely the space between the face of a FULLY closed bolt and the base of a FULLY chambered cartridge. It matters little what type of cartridge it is. I don't want to get into an argument about non-existant phantom points on the shoulder of rimless cartridges. No matter how you measure it in the final analysis it's still that distance between the bolt face and the cartridge base.

Zim

It seems like we had this same discussion not too long ago. The only problem with your definition is: how do you measure it? It's not a non-existance phantom point if you can measure it.

Ray

Although it is not the actual case, assume all cartridges have agreed-upon dimensions. One of those dimensions is the distance from the cartridge base to one of four other points on the case.



Those points may be:



1) the front face of the rim (in the case of most rimmed cartridges);



2) the case mouth (in the case of straight or tapered rimless pistol cartridges);



3) to some agreed-upon point on the shoulder (in the case of rimless, semi-rimmed, or rebated-rim bottle-necked cartridges).



4) the front edge of the belt on belted cases.



Headspace is simply excess chamber length (or depth) that allows a cartridge case, upon firing, to lengthen beyond this prescribed length.



Too much headspace gives the brass too much room to stretch, possibly rupturing the case and a leaking gas.



Too little headspace gives the brass no room to expand and/or "crimps" it into the chamber and can cause a pressure spike. (A good reason not to fire a round you had to force the action to close on)



A "tight" chamber is one with minimal headspace. A "loose" chamber has more headaspace than is desired and a Field Guage indicates it has an UNSAFE excess of headspace- in other words, there may be ammo out there made on the small side of acceptable ammo specs that is unsafe to fire in such a large chamber and may rupture.



As long as a mild headspace condition, whether too little or too much, is known, reloaders can adapt to it by simply resizing minimally but factory ammo dimensions vary.

You could use shim stock between the bolt face and the case or you could use a guage that measures to some point on the shoulder in a rimless case but the measurement still in either case is the distance from the case to the boltface. In PERFECT headspace the difference will be zero. My ordnance gauges for 30-06 which I have been using for 50 years are 1.940 1.946.1.950. that means from perfect to excessive is .010. Any way you look at it that .010 is the distance from the bolface to the case head.

Hello RonsGuns,

I too had a lot of questions about headspace. I read a lot of articles in several threads, until I came past this article. I hope it does for you what it did for me!

Tech Note


July 13, 2004



TECHNICAL NOTE 11: HEADSPACE



BACKGROUND: Few topics inspire as much interest and confusion as headspace. It is one of the few technical small arms terms recognized, if not understood, by even beginning shooters. It is seldom firmly understood by even experienced shooters.



FACTS:



1. In a narrow sense, headspace is the size of the cartridge chamber designed to accept a particular cartridge. Headspace is defined as minimum and maximum dimensions from the locked breech to either a contact surface or designated datum in the rifle chamber, or to the rear of the barrel. The points of measurement chosen depend on the type of cartridge case used (rimmed, rimless, semi-rimmed, or belted).



2. In a broader sense, headspace is a far more complex relationship between the cartridge, chamber, and firearm mechanism. The starting point for headspace is the cartridge case. The complex functions of the cartridge case include holding the cartridge components together, aligning the bullet in the bore, expanding to seal high pressure gasses, contracting in time for easy extraction, and removing heat from the chamber. Proper space for the cartridge allows it to function well. Improper space can cause dangerous pressure conditions at worst, or interfere with the function of the action.



3. Headspace ranges are established by industry advisory bodies, government bodies, or by individual manufacturers. In the U.S. the primary advisory body is the Small Arms and Ammunition Manufacturers Institute (SAMMI). Issues of producibility, safety, and mechanism reliability with a particular cartridge must be considered. Firearm manufacturers must produce firearms with chamber headspace that is producible, yet assures safe and reliable operation with all ammunition made to standard. This becomes an extremely difficult challenge when making self-loading firearms.



EXAMPLE: A .308 Winchester rifle with a SAAMI chamber, and ammunition made to SAAMI standard cartridge dimensions and tolerances reveals acceptable headspace ranges of:



Chamber dimensions: 1.630 minimum to 1.640 maximum (�reject�)

Minus case dimensions: 1.634 maximum to 1.627 minimum

Resulting headspace: .004 interference to .013 clearance



In this example, the SAAMI maximum headspace/minimum cartridge allowance produces so much clearance, .013 inch, that it will reduce case life. This much headspace would probably be found only on a used rifle. The SAAMI minimum headspace/maximum case condition produces .004 inch of interference that could make semi-automatic operation unreliable. The challenge for a manufacturer is to find a headspace range large enough to allow maximum interchangeability with reliable firearm function, and small enough to assure accuracy by aligning the cartridge in the chamber uniformly. Dimensions for new firearms should be equal to or larger than the SAAMI minimum to assure safety, but smaller than the SAAMI maximum to allow safe operation even after long years of use and wear.

4. Different manufacturers will sometimes set headspace dimensions different than those called for by advisory bodies. An excellent example is the 7.62mm/.308 cartridge:



CARTRIDGE DIMENSIONS MIN MAX

SAAMI .308 1.627 1.633

GOVERNMENT NATO 7.62 1.630 1.633



CHAMBER DIMENSIONS MIN MAX

SAAMI .308 1.630 1.640 (normal factory limit is 1.636) GOVERNMENT M-14 7.62 1.6355 1.6385

GOVERNMENT M-14 Match 7.62 1.631 1.633 (individually cut and non-interchangeable)



Note that the government MAX dimensions are for new guns and allows for future wear, while the SAAMI MAX dimension is the absolute limit of an acceptable chamber. ArmaLite�s current factory headspace dimensions for new AR-10B series are somewhat tighter than the M-14:



MODEL MIN FACTORY MAX REJECT

AR-10T 1.632" 1.636" 1.640

AR-10B, A4, A2 1.634" 1.638" 1.640



5. Gage manufacturers ordinarily produce headspace gages to the SAAMI specification defining "go" (minimum) as 1.630", "no go" (normal maximum) as 1.636", and "field reject" (the largest safe maximum) as 1.640�. It is important to note that technical issues define the headspace acceptable for each design, and that SAAMI�S standards are only a starting point. Customers often use SAAMI-based commercial gages to measure a firearm like an M-14 or an AR-10 and then declare its headspace wrong. That�s incorrect because SAAMI's .308 minimum is not optimal for many self-loaders like the M-14 or for AR-10s. Firearms frequently require custom headspace gages suited to their specific design.



MISCONCEPTIONS:



There are a number of popular misconceptions concerning headspace, notably that the tighter the headspace, the better, that loose headspace is dangerous, and that one particular dimension is best. None of these common beliefs is totally true.



Insufficient or excessively tight headspace tends to cause malfunctions such as failure to lock. It often makes extraction difficult and can cause dangerous stresses on the mechanism that shorten its life expectancy or lead to failure. Excessive headspace may lead to gas leakage around the case or head separation and the sudden release of high-pressure gas. Most shooters fear excessive headspace, but it is actually insufficient headspace that is more dangerous. A good firearm design can actually tolerate a great deal of excess headspace.



While the SAAMI example above demonstrates that a fairly wide range of dimensions work, manufacturers narrow their tolerances to conservative ranges that allow a reasonable combination of safety, reliable function, accuracy, and useful life.
Copyright 2004 ArmaLite Inc. All Rights Reserved

Actually you never really MEASURE headspace you merely CHECK it. You are not actually getting a decimal measurement of distance but a check to see if it is within tolerances. If the action/bolt/etc will close on a GO gauge and not on a NOGO gauge you don't actually know the distance just that it is within safe tolerances.

Cheechako, You specified the minimum car guage. If you had used the field gague you would have room for your tractor.
Good Luck!

Irv

Darn it Irv, you're right. Next time I have a garage built I'll specify field gauge.

z1r



You're right too. I forgot about my headspace thingy. I have one that fits over the barrel tenon with an attached dial indicator. Using it I can cut a chamber on a new barrel that is an accurate duplicate of the old one. I also have another thingy that measures the barrel tenon in a like manner. I have several benchrest rifles with glue-in actions and that is the only way I know of to make a duplicate barrel without being able to try the barrel in the action.



Ray

I think I like thingy beter than fixture. It kinda describes it more accurately, lol.

One final comment and then I shall consider never commenting again on this forum. I was also taught to use a depth mike to check the length of shank and distance to reciever internal ring on a M98 action. You can then measure to face of closed bolt and you have now established the distance the go gauge should protrude from the rear of barrel while chambering. True while the gauge measures to a point on the shoulder the important dimension is still the GAP between the bolt face and the cartridge base. All you are checking for when you use the Thingy and pull back on the bolt is this Gap. Most of MY bolts lift and don't pull back.

Zim

Please don't leave the forum over this. We agree on a lot, there is a certain amount of joking and kidding, and the things we don't agree on are simply differences of opinion. I think that's why most of us visit this and other shooting forums, to hear other guy's opinions. I'm an old guy and I'm still learning, or maybe I've just forgotten and lot of stuff and am learning it all over again.

Ray

Hey guys; I think there was a thread awhile ago on adjusting sizing dies for proper headspacing. I believe it said to start with the resizing die just touching the shellholder,then size a once fired case. Try to chamber the case,if the bolt is too tight or won't close turn the die down another 1/4 turn and try again. Repeat until the bolt closes smoothly. I tried this with a case and it worked very well. I'm sure I won't have to beg anyone to correct me if this procedure is incorrect.

Sure, but you may have started with the die too low if
touching the shell holder. I'd initally start a few turns
up and then work my way down, to get a "fit" just a wisker
past "a feel" on bolt close. Target shooting can be on the
"go-feel", but 30-30 type hunting stuff doesn't want to be
too firm.
John L.

So why instead of NO-GO , GO and FIELD aren't they called

SHOULDA KEPT REAMING, GLAD HE STOPPED REAMING, and DAMMIT! WHY DIDN'T HE STOP REAMING?!