Somebody explain Headspace.

Discussion in 'The Basics, Starting Out' started by summitsitter, Jul 2, 2008.

  1. summitsitter

    summitsitter Well-Known Member

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    Would somebody please explain what exactly headspace is, what purpose it serves in accurcy,how to measure,etc.I've read a few books but they get to indepth for me, so would someone please help.
     
  2. eddybo

    eddybo Well-Known Member

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    In simplist terms as I understand "headspace" it is the distance from the boltface to the shoulder. It is measured with go and no go gauges chambered as you would a cartridge. I do not think there is a specific correlation between headspace and accuracy, but there is a big correlation between headspace and safety.
     

  3. specweldtom

    specweldtom Well-Known Member

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    I'll take a stab at it too. When you load any cartridge into a chamber, there is a minimum usable distance between the bolt face and the base of the cartridge which will reliably allow the bolt to close. -- Go Headspace Gage--. There is more importantly, a maximum safe distance between the bolt face and the base of the cartridge, beyond which the gun can be dangerous. -- No-Go Headspace Gage--. Some cartridges are held in position in the chamber by the shoulder of the cartridge, example; .30-06, some by a belt, example; .300 Win Mag, some by a rim, example; .30-.30, and some by the mouth of the case, example; .45 acp, but all have a safe headspace range which will allow the cartridge enough room to chamber reliably, but not enough room to be dangerous.

    Summing up; a bolt or breechblock that will close on a Go Gage will accept all SAAMI std ammo for that cartridge. Good. Acceptable headspace. But... a bolt or breechblock that will also close on a No-Go Gage is deemed unsafe and should not be fired. Too much headspace.

    It's a good system, and there are few exceptions (The Field Test Gage for some military weapons and cartridges is one). This isn't a rule, but the difference between a Go and a No-Go gage is just a few thousandths, like .004" to .006" depending on caliber and cartridge.

    All cartridge firearms whether mass-produced or custom built have to fall into the prescribed headspace range for that cartridge. Custom builders in general will hold closer to the minimum headspace (Go Gage) for better brass life, possibly better accuracy, and just plain pride of workmanship.

    Hope this is not too long-winded, and is understandable, Tom
     
  4. Willys46

    Willys46 Well-Known Member

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    Not a Gunsmith

    I am not a gunsmith but like others will take a stab at it. I am sure one of the good gunsmiths on here with correct us.

    For my simple mind. i think of headspace as the distance from the bolt face to the center line of the shoulder for non belted cases.

    The belted cases are headspaced off the belt for SAAMI specs. but most people after the first firing of new brass headspace there reloads off the boltface.

    Too much headspace will allow the shoulder of the ammo to move to much and cause case head seperation. This is the resaon for a unsafe gun that has too much head space. Even if you do not get case head seperation, when you resize your brass you are over working it causing it to strech and get brittle.

    To little headspace and a round will not chamber..Just like when you reload a piece of brass and it becomes difficult to close the bolt. You need to push back the shoulder .002 or so, to allow it to chamber.

    I hope this helps.
     
  5. J E Custom

    J E Custom Well-Known Member

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    Summitsitter

    Headspace is primarily a safety issue as specweldtom stated
    but can have an effect on accuracy also.

    I will comment on the accuracy issue regarding headspace.

    No headspace is the best for accuracy but it is not practical
    for hunting,especially for dangerous game because of the need
    for multiple shots.

    If you start with a saami spec. loaded round it will have some
    headspace in the chamber. But once you fire it you will have
    no headspace with the fired brass and if you neck size only
    you will still have no head space.

    If you size the body of the case then you will again have some
    headspace depinding on how much you size.

    If the chamber of the weapon is true to the bore centerline of
    the barrel a fire formed case,neck sized only should align the loaded
    round with the barrel throat (The same as touching the lands with
    the bullet).

    When a loaded round is sized to go into the chamber easy it will lay
    in the bottom of the chamber (not aligned with the bore)until the bolt
    is closed forcing the round to square up to the bolt face.

    So the less headspace you have the better the alignment.

    On rifles with lots of freebore I like to use less than .001 headspace
    to force the round to square up in the chamber

    Reloading is much easier with .003 or .004 headspace but by reducing
    headspace and carfull reloading the accuracy should improve.

    Safety comes first then accuracy
    J E CUSTOM
     
  6. Long Time Long Ranger

    Long Time Long Ranger Well-Known Member

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    I thought it was the empty space measured between the ears and the brain. Some seem to have quite a bit more than others. Particularly noticed with drivers during rush hour traffic. In a rifle proper headspace keeps the firing pin from driving the case forward when it strikes the primer which can be very dangerous from hangfires to blowing up. With belted magnums the rim of the belt stops forward motion by matching the corresponding cut in the chamber the proper distance from the bolt face with a go-no go gauge. With non-belted cartridges the shoulder of the cartridge stops the forward motion so the headspace is measured to that point from the bolt face with a go-no go gauge. Maybe when enough of us describe the same thing all in different terms those of us with the greatest headspace can even understand it.
     
  7. Eaglet

    Eaglet Well-Known Member

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  8. summitsitter

    summitsitter Well-Known Member

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    Eaglet thanks man that's just what I was looking for.
     
  9. boomtube

    boomtube Well-Known Member

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    Discussions of headspace tend to be confusing because the speakers often go too soon to how it's measured without a clear explaination of what it propery is.

    Simply stated, "headspace" is where the cartridge sits in a chamber. Eagletts drawings clearly illustrate that. If there is too little headspace the action cannot be closed on a standard cartridge case. If the headspace is too great, the case will move too far forward in the chamber and a lot of non-funny things become possible with firing. Headspace is measured from the bolt face to the part of the chamber that prevents further forward movement of the case.

    Almost everyone knows rimmed cases headspace on the rim itself so a case body that fits somewhat loosely in the chamber is not, of itself, a hazard. Ditto with belted cases, belts are actually sort of funny looking rims. Rimless, or rebated, cases must stop their forward motion on either a shoulder (bottle necked cases) or on the mouth of the case (straight walled cases).

    There are different ways of measuring it but headspace gages are not very good, they don't actually tell us WHAT the headspace is, only if it lies between a specified minimum and maximum length. I want to know if my chambers are on the minimum or maximum side of that specified range so I can set my FL dies accordingly!

    Perhaps those tools that measure fired case lenght to the shoulder, on bottle neck cases anyway, are best for measuring true headspace, it will be perhaps a thousanth or two more than the measured length because of brass spring back after firing. I believe the "Precision Case Mik" tools from RCBS are perhaps the easiest way to measure the location of a fired - or resized - rifle case's shoulder. The Sinclair and StoneyPoint/Hornady case gages are close seconds.

    Sinclair sells chamber length gages, small cylindrical brass pieces to be seated in place of a bullet, which can be used to measure the OAL of a chamber. Rifle chambers are typically 20-30 thousanths longer than minimum so that is good info for case length trimming but it only relates to headspace, as such, for straight sided pistol cases.
     
    Last edited: Jul 11, 2008
  10. J E Custom

    J E Custom Well-Known Member

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    Quote:
    There are different ways of measuring it but headspace gages are not very good, they don't actually tell us WHAT the headspace is, only if it lies between a specified minimum and maximum length. I want to know if my chambers are on the minimum or maximum side of that specified range so I can set my FL dies accordingly!




    I would have to strongly disagree with the statement that head space gauges are not
    good for measuring head space.They are the best way, because they are SAAMI specs.
    and all gunsmith and manufactures use these to set up a weapon to operate safely.

    And to find out what your "actual" head space is very simple, First start with a Go Gauge
    of the same cartrige designation.

    Then add a brass or stainless shim .001" thick to the front of the bolt face.( a small piece
    that will set flat on the bolt face can be held on with a touch of grease).

    If the bolt closes go to a .0015" shim and repeat process. If it will still close go to a .002"
    shim.

    If it will not close on .002" but will on .0015 then .0015 is your actual head space over
    the minimum SAAMI spec.


    Quote;
    Perhaps those tools that measure fired case lenght to the shoulder, on bottle neck cases anyway, are best for measuring true headspace, it will be perhaps a thousanth or two more than the measured length because of brass spring back after firing. I believe the "Precision Case Mik" tools from RCBS are perhaps the easiest way to measure the location of a fired - or resized - rifle case's shoulder. The Sinclair and StoneyPoint/Hornady case gages are close seconds.



    These tools are for measuring fired or sized cases as there name implies.

    There are other ways to get close but I would use these to check fired cases against sized
    cases but not headspace.

    Just my opinion
    J E CUSTOM
     
  11. Long Time Long Ranger

    Long Time Long Ranger Well-Known Member

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    Thanks J. E. We could write a book on this but I think his question was answered. Like J E says their are a number of ways we get the headspace where we want it.