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What is head spacing?

Discussion in 'Rifle Country' started by mopar92, Jun 8, 2011.

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  1. mopar92

    mopar92 Member

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    I understand fully how complex it must be based on gunsmith's talking about it. Just for my knowledge, I don't recall any part of a gun called "head" , so in short, what is it and how is it measured? Thanks!
     
  2. briansmithwins

    briansmithwins Member

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  3. Walkalong

    Walkalong Moderator

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    A simplistic answer is how much slop, or play, front to back, the round has when it is in the chamber.

    Headspace is machined into the firearm. It has a min and a max.

    Cartridges are loaded to specs, min and max, such that if they are chambered in a properly headspaced firearm, the slop, or play, front to back, will be minimal, and safe.

    If we push the shoulder back to far on a bottle necked caliber such as .30-06, we can create artificial, but still dangerous, excessive headspace that could cause a case head separation.

    We cannot create artificial headspace on a rimmed pistol caliber such as .38 Spl, because it headspaces on the rim.
     
  4. mopar92

    mopar92 Member

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    Understood... Thanks
     
  5. caribou

    caribou Member

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    That is why headspaceing in a Mosin Nagant rifle is not a big issue, and they are rarely out of 'spec' with each other, as the cartridges are all manufactured to a certan specification.

    I worry much more about the firing pin protrusion on a rimmed cartridge when I first aquire them, especcially refurbs, but generally ,even changing bolt heads on rimmed rifles isnt a big deal..

    With rifles that headspace from shoulder to bolt face, if the bolt is not a numberd match, I check it, if possible.
     
  6. MIgunguy

    MIgunguy Member

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    Thank you!! I've been wondering the same thing myself and could never figure it out.
     
  7. jpwilly

    jpwilly Member

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    When you forget what you were doing...
     
  8. mopar92

    mopar92 Member

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    Why not worry about a Mosin and worry about an AR? In terms of cartridge? You'd think Russian stuff would be more out of spec...
     
  9. HoosierQ

    HoosierQ Member

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    Mosin fires a rimmed cartridge I guess.
     
  10. caribou

    caribou Member

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    Manufacturing ammo to certain specifications has always been as important as manufacturing firearms to spec. The two must work together flawlessly, despite who or whom made them, and they ammo must work in each and every gun its designed for.
    Russia has made reliable ammo and guns for decades....reliable for sure, maby not as accurate/consistant as they could have,I think, but to them, quantity had a quality all its own.



    There is no "Head" on a gun, its a reference to the "head" of the cartridge, usually the area that makes up the base of the cartridge, where the rim, or clenature(groove) and 'rimless' rim are ( where the area grabbed by the extractor ('rim'~lOL!~) including the surface where the 'head stamp' is that gives cartridge manufacture info, usually in symbols, letters and numbers, and the primer pocket itsself.
    Funny, catridges stand on their heads, but their shoulders are on the other side of their bodys.....
    Anyway, forces genereated during propellent burning are exerted against this area and the force is called "Case head thrust', the equall and opposite force that is propelling the bullets down the tube......
     
  11. TexasRifleman

    TexasRifleman Moderator Emeritus

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    There is no problem with rimmed cartridges because they are already held flush against the rear of the chamber by a physical barrier, the rim.

    Rimless is where you run into problems. If the chamber has excessive headspace the round is not up against the bolt face necessarily when fired. This causes the case to stretch rearward which isn't really where cases are designed to stretch. If they rupture, pressure can be released in a dangerous direction. Cases are generally meant to stretch outward tight against the chamber walls to contain this pressure, not stretch in overall length very much.

    If a chamber is excessively long with a rimmed round all you get is the shoulder area blown out. This can ruin the brass, but it really doesn't present any danger because the pressure is still contained in the chamber and released out the bore.
     
  12. MtnCreek

    MtnCreek Member

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    But with rimed cartridges, if there's excessive space between the boltface and head, there is still excessive headspace regardless of how long/tight the rest of the chamber is. Correct?
     
  13. TexasRifleman

    TexasRifleman Moderator Emeritus

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    Headspace is the excessive space in FRONT of the cartridge that can allow a round to move too far forward. Since that can't happen with rimmed rounds that excess space really doesn't cause any problems. It can ruin brass (with necked rounds) because the shoulder area gets stretched out, but it doesn't cause a dangerous condition because it doesn't release pressure in a dangerous direction. And of course with straight walled cases it does nothing, which is why you can fire .38 Special in .357 chambers for example.

    If there is space between the bolt face and the case in a rimmed cartridge firearm that is not excessive headspace, that's another problem entirely.
     
  14. Walkalong

    Walkalong Moderator

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    Excessive headspace in a revolver with rimmed calibers is rare, but not dangerous. Worse case scenario is the firing pin can't reach the primer well enough to set it off. To little headspace and the cylinder won't want to close. Again, not dangerous. Frustrating, but not dangerous. Also rare.

    If the gun has been abused there could be excess space there, but it isn't a headspace problem so to speak, but a worn/damaged parts problem creating artificial headspace.

    Yes, in the rare instance there is excessive headspace in a revolver, the rest of the chamber has no bearing on it.
     
  15. MtnCreek

    MtnCreek Member

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    I was under the impression that headspace was measured from the bolt face and a rimmed cartridge is measured from boltface to rim. A rimmed cartridge with proper headspace between bolt face and rim, also having an out of spec chamber would still be considered properly headspaced, even though the chamber is out of spec (potentially causing other problems).

    If there is too much space between the rimmed cartridge case and the bolt face, then the case is the structural support for the pressure generated during firing; not just the gas seal as intended and a rupture of the rimmed case would release gasses in the general direction of the shooter. Right?
     
  16. TexasRifleman

    TexasRifleman Moderator Emeritus

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    Yeah, that's my understanding as well. When something technically becomes a headspace issue or whatever other name game doesn't matter and I probably misuse the terms, but what you say right there is the gist of the whole thing.
     
  17. mopar92

    mopar92 Member

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    Interesting. How is it adjusted if, let's say, you build your own AR? Do you shim something to get that spacing down? What if the bolt is shut, and there is too much head spacing?
     
  18. TexasRifleman

    TexasRifleman Moderator Emeritus

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    ARs, because of their design, are actually pretty hard to set up so that you have headspace problems. That's assuming all the parts are manufactured correctly and within spec of course. Some people will say they are "Self Headspacing" but I don't think I'd use that term.

    The bolt lugs lock into the barrel, that sets the headspace. That's why with all the parts manufactured right there is little chance of a problem.

    Unless you have worn out bolt lugs, or some problem with the lugs in the barrel, you really don't have much to worry about unless the chamber was reamed wrong.

    That said, if you build your own upper you should always run a GO/NO GO set in there just to make sure, but it's not nearly as big an issue with ARs as with other designs.

    If you have a chrome lined barrel you can't really change it. If it's an unlined barrel a gunsmith can ream the chamber a bit if headspace is too short. If it's too long really all you can do is try a few different bolts and hope one shortens it up, or toss the barrel. Do NOT ever try to lengthen headspace by taking metal off the bolt, that's a recipe for disaster.

    If I am mistaken I know the AR experts will be along to correct me, but that's always been my understanding.
     
  19. Zach S

    Zach S Member

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    Headspacing is to rifles, as ring gap is to engines...

    And yes, you can ream an AR chamber in a chrome lined bbl. Michiguns LTD (makers of the MOACKS tools) explains this in a little more detail on the website.
     
  20. caribou

    caribou Member

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    You can set headspace in (most) bolt action rifles by tightening, loosening or removing material from the barrel (reducing barrel face or deepening the chamber)and reseating it.
    I think I used shimms to set the barrel to reciver and bring my Inch FAL to proper headspace....and used different sized rollers to set the head space on my H&K , when I wacked the kit together.
     
  21. bigedp51

    bigedp51 member

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    Excess head space. :rolleyes:

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    More than acceptable head space.

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    Animated Enfield .303 British head space.

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    Half inch of head space. :eek:


    [​IMG]

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    Types of head Space

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    [​IMG]
     
  22. caribou

    caribou Member

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    Great post bigedp51,
    if excessively headspaced on the rimmed cartridge, just a bit ~LOL!~ it takes some jacking or damage to find a mass produced rifle that has a universal headspacing sizing based on production ammunition, military wize, to be excessevly headspaced, but it is true, in some strange ways, these things can happen..... Like finding a Russian AK that cannot accept a Russian made AK magizine....pretty rare allright, but ..........


    Maby you can answer me a question here ....

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    [​IMG]

    So ya think I should stop using Remington .308's in my 30-06 and switch to Winchester .308?

    ~~LOL!!~~
     
    Last edited: Jun 10, 2011
  23. scythefwd

    scythefwd Member

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    Tex - you shave the face of the barrel until it is in proper specs. Most barrels, that aren't drop in, are chambered too deep by a few thousandths or so. When you install the barrel, you then shave the face of the barrel off to create the proper head spacing for the chambered round. That is, after you have threaded the barrel shank (basically talking either a tapered, and chambered blank or a chambered blank).
     
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