I'm wondering why one can't just use an unfired, brand new, factory rifle case (or several), to set head space when rechambering, setting back, or installing / reaming / fitting a new barrel? It seems that when I hand load neck sized brass in my rifles that I will get just the faintest resistance when chambering a round in my bolt action or sliding block single shot rifles. It seems like that would give you an effective .000" head space with the bolt face contacting the head stamp of the cartridge case. I've never actually tested that bolt face to head stamp contact but am pretty sure that it exists. Maybe "prussion blue" or something would be used to check for good contact?

I know that gunsmiths always use head space gauges (go and/or no go) to set head space, but why can't a new unfired factory cartridge case be used instead? Seems like you would always start out with .000" head space that way. I'm sure there is probably some good reason NOT TO DO THAT, but am just wondering what that reason might be. I'm hoping that some benevolent gunsmith will enlighten me on this.

Rev

I think you'll find that factory cases are shorter than minimum headspace. To make a long story short, a friend bought a used Savage 110L that we figured was about .004" short. It won't come close to closing on a GO gauge and we resized with an .006" feeler gauge under the case head. Most factory ammuntion would chamber with some resistance. A Forster GO gauge is $26.00, well worth it IMO.

http://www.forsterproducts.com/Pages/gages.asp

Bye
Jack

A fired case will shrink a tiny bit. When you fire a round, the case is literally welded to the chamber for an instant but cools and shrinks down a fraction. A guage is more precise and will not have any crush like brass does...the gauges really are better.

I think you'll find that factory cases are shorter than minimum headspace. To make a long story short, a friend bought a used Savage 110L that we figured was about .004" short. It won't come close to closing on a GO gauge and we resized with an .006" feeler gauge under the case head. Most factory ammuntion would chamber with some resistance. A Forster GO gauge is $26.00, well worth it IMO.

http://www.forsterproducts.com/Pages/gages.asp

Bye
Jack

I didn't really mean to question the price of the head space gauges and what you say makes perfect sense value/$$$. Are you saying though that when firing virgin brass that .004"-.006" of case stretch will likely occur? I guess if that happens once it may be OK. What about the guy (Rocky?) that full length sizes every time? Seems like that .004-.006" case stretch would add up pretty quickly to case head separation. I do realize that most full length sizing dies don't really return the case to factory dimensions (except for small base dies), but it still seems like the amount of head space left by those extra short cases might be a problem.

Rev

Rev, If you were to measure several differnt lots of cases from the same manufacturer's there would be an inconsistency in all demensions and even greater differances between manufactures. Sammi specs more or less hold the middle so that all cartridges will work in all chambers. That is why you have that head space for larger cases. Too much head space is bad and you might have a case blow out at the webb. You could use a unfired case for a gauge, but you should reload all your rounds and you should use that fired cases demenitions as the base for all you reloading in that chamber only. There to much data to go over here. Read the book by Earl Naramore if you can find it ,called, Principles and Practice of Loading Ammunition. Bobby
I should have stated also that you should use that fired cases demenisions as you base for reloading and not resize to the unfired. your chamber is now your specs for reloading providing that the case that you started with is not one that is on the short side. I think that most reloaders only neck resize and not fully resize there cases. this way your cases are sized exactly to your chamber and will give you better accurcy and longer case life. Your cases will grow in all demenisions from repeated firing untill you will have to full resize depending on the loads that you use, and how many firing you will get depends on the loads.
I said all that to get to this, in the book by Naramore he says "It is now possible to postulate three conditions that pertain to the relationship that exists between the cartridge case and its chamber and which affect the case when it is fired.
(1) All cartridge cases of a kind differ from one another in their deminisions within certain maxium and minimum limits.
(2) All chambers for the same cartridge differ from one another in their dimensions within certain maximum and minimum limits.
(3) Any maximun cartridge or cartridge case will enter easily into any minimun chamber intended for it." Ch.4, pg.54 That is the reason for a head space gauge. To make things as uniform as possible for the sake of safety. I'm done and out of here. Bobby

Rev, If you were to measure several differnt lots of cases from the same manufacturer's there would be an inconsistency in all demensions and even greater differances between manufactures. Sammi specs more or less hold the middle so that all cartridges will work in all chambers. That is why you have that head space for larger cases. Too much head space is bad and you might have a case blow out at the webb. You could use a unfired case for a gauge, but you should reload all your rounds and you should use that fired cases demenitions as the base for all you reloading in that chamber only. There to much data to go over here. Read the book by Earl Naramore if you can find it ,called, Principles and Practice of Loading Ammunition. Bobby
I should have stated also that you should use that fired cases demenisions as you base for reloading and not resize to the unfired. your chamber is now your specs for reloading providing that the case that you started with is not one that is on the short side. I think that most reloaders only neck resize and not fully resize there cases. this way your cases are sized exactly to your chamber and will give you better accurcy and longer case life. Your cases will grow in all demenisions from repeated firing untill you will have to full resize depending on the loads that you use, and how many firing you will get depends on the loads.
I said all that to get to this, in the book by Naramore he says "It is now possible to postulate three conditions that pertain to the relationship that exists between the cartridge case and its chamber and which affect the case when it is fired.
(1) All cartridge cases of a kind differ from one another in their deminisions within certain maxium and minimum limits.
(2) All chambers for the same cartridge differ from one another in their dimensions within certain maximum and minimum limits.
(3) Any maximun cartridge or cartridge case will enter easily into any minimun chamber intended for it." Ch.4, pg.54 That is the reason for a head space gauge. To make things as uniform as possible for the sake of safety. I'm done and out of here. Bobby

Thanks Bobby, you said what I was trying to say, but about 1000% better. I was of course talking about the same chamber and neck sizing (partial sizing minimally when necessary) with a full length die. I basically want my bolt face smack dab up against the head stamp of of my loaded cartridge. I want a slight resistance when chambering a round. I can't really see that it matters what the minimum/maximum dimensions of the factory chamber or the factory brass is as long as my cartridges are custom fitted to my chamber.

I really don't care if someone with a different rifle/chamber can fire or even chamber my rounds. That's what I was trying to get across in my original post. Thanks for making clear what I was trying to say.

Rev

For all cartridges which are standardized by SAAMI, a set of drawings are issued. These are for maximum cartridge and minimum chamber. The drawings specify the various dimensions and their tolerances. The headspace dimension on both drawings is the same, and this is what is used to grind a GO gauge. Headspace specs for the cartridge drawing allows a certain amount of minus tolerance, thus establishing what the minimum cartridge will be. The tolerance of the chamber drawing is in the plus direction, thus setting the maximum chamber dimension. As stated above, the object is to be sure that all cartridges of a particular caliber will fit in all appropriate chambers, and will safely function in the gun.

Using a cartridge in place of a GO gauge would result in a chamber of some dimension smaller than that which would result from using the gauge, and another lot of cartridges might not chamber in the gun. You are always free to resize your cases to the minimum that will custom fit in your gun, and this will usually mean long case life.

The NO GO gauge is the gauge used to check that the chamber on a new barrel will not have been reamed too deep. Thus, a proper chamber job should accept the GO gauge and reject the NO GO gauge. The difference between these two gauges on a centerfire rifle is usually in the nature of .004". For a rifle which has been in service, the FIELD gauge is used to assure that wear has not put the headspace past the SAAMI spec for the max chamber.

Headspace and headspacing is a nebulous subject and there are myriad reasons and descriptions and explainations on the subject...but it isn't a cast in stone thing.

There are legal issues, wants and desires, different interpretations and so forth.

A gunsmith stays within SAMMI specs so the customer can shoot just about any ammo he can lay hands on in any country in the world...within reasonable limits.

A person seeking the maximun case capacity might opt to keep his chamber at maximum dimensions as well as the reloading dies.

A target shooter might opt for minimum limits to keep dimensions as tight as possible.

To get "zero" headspace is relatively easy as far as machining goes...BUT YOU will have to do quite a bit of work on the brass...squaring the base, making sure the length from datum point to base is identical in all cases which entails facing the base of the case and also having a measurment gauge at a minimum and way too much work for the average reloader and not needed for anything but target/benchwork to get maximum accuracy anyway.

Having a minimum of plus 0.006" headspace lets you shoot almost any case with a minimum of futzing around...PLUS you can easily adjust headspace with a set of Redding Competition Shell Holders within a 0.002" range per shell holder and Redding will cut you a shell holder of plus dimensions for a small fee. 0.006" is a very small amount if you've ever mic'ed that amount...basically equal to two sheets of paper or a grain of sand to lock it up tight as a.........

On a custom rifle you can dictate headspace to your gunsmith...within his legally defined parameters...on a factory rifle you get whatever is allowed or whatever happens to come out...within certain parameters.

And there are always the issues of functionality. Almost all factory ammo that I've ever used (not a whole lot as most of my rifles have custom chambers and headspace)is manufactured closer to the minimum SAMMI length and below so it will function in just about any rifle out there. If you want an eye opener just measure a box with a Stoney comparator. I've shot ammo that had 0.025" difference between unfired and fired factory ammo in several rifles and calibers. It all worked without a hitch, had hunting accuracy and I never had any problems with reloading the brass...after I adjusted the sizing die and shell holders to fit the chamber dimensions. Some "Match" ammo also had a bullet runout range of 0.000" to 0.020". It shot alright and with better accuracy than the "cheap stuff" as long as the cartridges were arranged in some order keeping the runout in ascending minimum range order.

The issue of headspacing...maximum or minimum and the reasons to select is...for the most part...better left to the gunsmith for the average hunter, with minimum discussion on the customers part...and as part of the reasoning process for the more advanced and experienced shooter. This is not to say "take whatever you get, shut up and sit down", I'm saying there is a lot more going on with all the parameters than 85% of all shooters ever understand or want to for that matter, and encompasses the rifle as a system...including all the variables of reloading, scoping, stocking, barrel type, length and material, actual intended use, caliber and case size and type and so on. An excellent gunsmith already understand this and much, much more, so can guide you toward the best solution.

So...headspace can be nothing simpler than what Bobby or QuarterChoke stated or as complicated as what a highly competitive benchrester is interested in...and/or everything in between.

'Njoy

Taking a break so I will add an illustration by way of actual happenings.

I have two projects going on right now...a 9.3x62 on a VZ-24 action with a Lothar Walther "prefit" barrel. The barrel came chambered deep by 0.022" using a PT&G 9.3x62 go gauge. The other project is a 375 H&H, ER Shaw Barrel for a Savage 110 LA, chamber depth doesn't matter on this one as long as it isn't beyond SAMMI specs.

The 9.3x62 RCBS FL sizing die sized a necked up 35 Whelen case to 4.094" measured by a Stoney #400 gauge using a standard RCBS shell holder. The GO gauge measured 4.109" by the same Stoney gauge. I don't like to work my brass hard so I stay within 0.003" to 0.006" headspace depending on what the rifle is going to be used for, the type of action, how easy it is to adjust headspace and so on.

The important numbers for me is the FL sized case length number - 4.094" and the finished chamber length fired case length number - 4.010"...0.006" headspace and for this rifle just right...but 0.009" "short" if you go by SAMMI specs - 4.109" go gauge. Not a lot of shoulder set back and easily adjusted using a +0.002" or +0.004" Redding Competition Shell Holder...I won't bother as these 50 cases will last longer than I will.

The difference between the sized case of 4.094" and the go gauge of 4.109 is 0.015" so if I had just headspaced to the go gauge dimension without any thought, I would be working the brass 0.030" every time I fired one, (one cycle of sizing and firing) or I would have had to use Redding Competition Shell Holders (which I use all the time anyway due to the difference between chamber and sizing dies).

I don't use factory ammo as I said before but even so I would bet I wouldn't have any trouble with most brands if I wanted to pay the freight...someday I might try some factory ammo just for kicks.

On the 375 H&H the usual method is to headspace on the belt...but if you have ever measured the belts on several brands of brass you would see that the "standard" 0.220" headspace for belted magnums has a varience also. I've measured different brand belts from 0.214" to 0.224"...that's 0.010" range.

Here again...I pick a brand of brass, buy 100 cases, then measure a case sized in the die that will be used...no borrowing here...I then set the barrel to headspace on the shoulder of the sized case...NOT THE BELT...sometimes adjusting by grinding off the bottom of the die, or using Redding Comp Shell Holders to achieve the desired results. I can get 5 reloads (my maximum for most cases) from any of my belted mags without any problem and most will go more.

Maybe this tome will help...maybe it will confuse...hope it helps. Headspacing is a controversial subject subject to the whims of the players. If I were 'smithing for a living I would be using SAMMI specs just to CYA and if that wasn't acceptable to the customer then he wouldn't be...

'Njoy

From the above posts, it seems that the conventional "go","no go" tolerances are necessary to insure that any factory cartridge will in fact function in any factory chamber. I can certainly appreciate how that might be a necessity for factory production of firearms or ammo. I can also see how these tolerances can affect an individual gunsmith where legal issues and $$$ might crop up when building a custom rifle.

I cannot see why minimal SAMMI dimensions (+/- .0005") cannot be utilized for a custom chamber? The tooling is available to do that, isn't it? I also cannot see why a gunsmith would not want to discuss head space dimensions with a perspective customer, unless he was just not capable of delivering that afore mentioned minimal head space to .0005" tolerances.

Not meaning to criticize gunsmiths or manufacturers. I certainly recognize that closer tolerances take more care and time, better tooling, and therefore, cost more $$$. It does seem like some who responded here advocate a "my way, or the highway" approach. That just does not seem like a reasonable (or profitable) approach to me.

Rev