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Thread: Headspace

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  1. #1
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    Headspace

    In light of realizing that so many good folks are misinformed on the subject of correct headspacing in the 1911 pistol, I took the liberty of doin' this thread in the interest of our continuing education, so that all may be armed with the knowledge to make a call of: "SHEEPDIP!" whenever some gunshop
    commando drops a round into a barrel chamber...shows that the rear of the rim is flush with the face of the hood...and pronounces it good to go. While that condition may well exist in a pistol with perfectly acceptable headspace,
    that, in and of itself, is NOT an indication.

    Headspace falls into two categories.

    Static headspace is the measurement between the breechface and the cartridge stop shoulder with the pistol in battery. Static headspace only changes with wear and/or locking lug deformation or setback...or wear on the breechface.

    Live...or working headspace is the difference between that measurement and the length of the cartridge case that is fired in the gun...and varies with every shot unless all brass is trimmed to exactly the same length.

    Excessive headspace is defined as static headspace that falls outside of acceptable limits as set by the SAAMI for the caliber. Static headspace is correctly determined with a gauge...typically GO and NO-GO. Precisely measuring headpace requires a determination of the exact dimension, usually done by using a GO gauge and an appropriate feeler gauge in conjunction.
    GO...plus feeler gauge thickness equals total static headspace.

    Headspace limit for the 1911 pistol is .898 inch minimum and .920 maximum. GO and NO-GO sets are made to these specifications.

    Headspace can be excessive and still be safe. It can be excessive and be dangerous. It depends on which direction that the excess goes.

    If the stop shoulder is reamed too deep in the chamber, it can be outside ot the maximum limit, yet still be safe. If the locking lugs are incorrectly located,
    incorrectly cut, or deformed...the excess can be dangerous , because it allows partial opening of the breech on firing. The case backs out of the chamber until the slide reaches the limit of its rearward travel as determined by the horizontal lug to lug fit...and the case head loses chamber support.

    You can ream the chamber too far...file the hood to perfectly flush with a chambered round or GO gauge...and it will look like good headspace...but it's not.

    You can ream the chamber perfectly at minimum dimension...with a cartridge
    or GO gauge dead flush with the hood face...and if the lug fit allows the breech to partially open beyond NO-GO limits on firing, you have a dangerously excessive headspace condition.

    To better understand this, we need to understand that when the pistol fires, the slide and barrel are tied together by the horizontal lug engagement. The barrel is slammed forward by the bullet while the thrust of the expanding gasses are driving the slide rearward in a 20,000 psi tug of war...and are doing their level best to separate the slide and barrel. If the lugs allow the slide to move rearward beyond safe limits...NO-GO...the case follows the breechface...loses chamber support at 6 O'Clock...and bulges or blows.

    Hope this clears things up a little.

    Carry on!
    Last edited by 1911Tuner; 13th December 2005 at 05:34.


  2. #2
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    If you have a fired but sized casing of a determined length, could you use that number and feeler gauges to measure headspace, by inserting the case into the barrel and using the feeler gauges between cartridge and breachface?
    Because I hit what I aim at, that's why.

  3. #3
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    re:

    Quote Originally Posted by AnthonyRSS
    If you have a fired but sized casing of a determined length, could you use that number and feeler gauges to measure headspace, by inserting the case into the barrel and using the feeler gauges between cartridge and breachface?

    Yes. The caveat is that you have to be careful when using the feeler gauges.
    Start the gauge between the breechface and rim from the underside with the barrel slightly out of battery position, and push it upward in the slide. The gauge should pull out with just a little drag. When you get close, you can use a strip of paper along with the gauges. Typing Paper averages about .0045 inch thick. If the paper tears without slipping, it's .003 inch...if it slips and then tears...it's about .002 inch. If it slips without any drag, it's over .005 and if it slips and comes out just as it starts to tear, it's .004 inch.

    A fired, resized case whould be used to prevent drag on the chamber walls, and possibly giving a false reading. The mouth should also be as square and true as you can make it by using a case trimmer. The case mouth may "give" or deform a little when the feelr gauge makes it a tight fit, and prevents a really accurate measurement...but you can get pretty close with a little practice.

  4. #4
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    Thanks for the very useful info - and great .sig by the way. I do Malinois rescue....

    Matt

  5. #5
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    Rescue

    Quote Originally Posted by MattLarson
    Thanks for the very useful info - and great .sig by the way. I do Malinois rescue....

    Matt
    Ah! Love the Belgians! My former neighbor had a pair of magnificent Turvurens. Good work on the rescues. Wish there were more people lookin' after our best friends instead of so many who treat'em like they can't think or feel.

  6. #6
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    Quote Originally Posted by 1911Tuner
    Ah! Love the Belgians! My former neighbor had a pair of magnificent Turvurens. Good work on the rescues. Wish there were more people lookin' after our best friends instead of so many who treat'em like they can't think or feel.
    Just transported a rescue last weekend, a three year old Mali boy who was just scared to death. Felt so bad for him. He was an owner give-up for the lame reason that the owner's mother had been bitten by a German Shepherd and would not come to visit if the dog was in the house.

    He's made his way to his foster home now, on a horse farm with three other Belgians to play with

    And yes, I was carrying my Kimber when I transported him (knew there had to be something gun related in here )

    Matt

  7. #7
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    Would safe headspace be affected when the lower lugs of a 1911 barrel has been abuselly battered and that the slide is no longer flush with the frame at the hammer area?
    Walk slowly, speak softly and carry a big stick!

  8. #8
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    re:

    >Would safe headspace be affected when the lower lugs of a 1911 barrel has been abuselly battered and that the slide is no longer flush with the frame at the hammer area?<
    ****************

    No

  9. #9
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    Headspace question

    I've read the excellent headspace sticky. A part I didn't see discussed, and which seems important, is the relation between the minimum chamber depth (distance from the deepest part of the feed ramp cut into the chamber of the barrel to the shoulder), and the headspace(s).

    This minimum chamber depth, and headspace, combined with the timing, look like the critical safety factors.

    I'm probably missing something (nothing new). Can we say that a pistol with a minimal static and live headspace would be more tolarant of a shorter, or less supported chamber (deeper ramp into chamber) than would a longer headspaced gun - given proper timing in both situations. Same barrel.

    Would case length matter? I cannot see where it should.

    For example, a gun with static of .900 and live of .903. It SEEMS, if the gun is properly timed, that there is up to an extra .017 of room in the chamber which could be used to safely deepen the barrel ramp.

    The example I can think of where this might be useful is for something like the Kimber ramp the dremmelheaded gunsmith Dremmeled in that other sticky. But I'd like to understand the relationships.

    If that gun had the headspace dimensions above, and it were properly timed, could you use all or any part of the .017 to move the barrel ramp forward into the chamber to get it away from the ramp ledge? Safely?

    Thanks, yet again. Learning never ends. Nor, with luck, curiosity and interest.

  10. #10
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    Chamber Ramps

    Well...With all dimensions at or near minimum, assuming that the barrel is truly within spec...you could probably get away with a bit more than that, but it's not advisable, nor is it recommended. Case webbing and wall thicknesses vary a bit from one manufacturer to another. A given amount of unsupported area may not cause a problem with one brand, while another would produce a noticeable bulge forward of the web when fired in the same gun. PMC ball for instance, will tolerate quite a bit of unsupported area...while Federal won't. Not knocking Federal. It's good ammo, and not prone to case head failure as long as the headspace is within allowable tolerance. It's just that PMC has a slightly longer web, and is thicker ahead of the web...so it doesn't bulge as readily as Federal when fired in a gun with less head support.

    So... .017 inch to play with may be okay with some ammo brands in a given gun, but not with others. As long as you maintain control of the ammo, you can probably get away with it...for a while.

    This was mainly intended to be a general overview, meant to explain that dropping a cartridge or a GO gauge into a chamber is not a reliable indicator of good or safe headspace...since many seem to believe that because the rim sits flush with the barrel hood, everything is good to go.

    Due to its relatively low operating pressure, the standard .45 ACP cartridge is pretty forgiving of headspacing...but it's not without limits.

    Also, as noted...You can have a minimum chamber with zero headspacing...and still have insufficient case head support. You can have a gun that goes to battery easily on a maximum gauge...NO GO...and still have perfectly safe case head support. The dimension from chamber face to stop shoulder figures in. The angle of the barrel ramp is a player, too. Nothing is everything...Everything is something. Tolerances stack.

    Finally...as also noted...Working headspace grows with use. Barrel and slide lugs deform and wear. As they do, the barrel and slide are driven further and further apart when the gun is fired. What starts out as .017 inch when the barrel is new, can grow to be .020 inch or more...and how soon depends on
    the ammo and the amount of use the gun sees, and how well the barrel fits in the beginning. If it's closely fitted and held in solid contact with the slide lugs, it'll take longer. If there's .010 inch of fore/aft play, it'll happen sooner, because the barrel and slide "slap" when the pressure hits and drives them in opposite directions. The amount of barrel movement is generally the amount of breech opening while under pressure. You can see how that works by holding the barrel forward firmly with your finger while puling back on the slide until the slide stops without moving the barrel. If the slide moves .010 inch without moving the barrel...the breech is opening that much when the gun is fired, and the case backs out of the chamber that same amount. If the barrel starts to move as soon as the slide moves...it doesn't open under pressure, and the case doesn't back out.

    So...if you use that extra .017 inch AND the breech opens .010 inch...you have .027 inch of unsupported case head area...and it tends to grow with use.

    Hope this helps.

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