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Thread: how to use headspace gauges?

  1. #1
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    how to use headspace gauges?

    I built an upper with a kotonics/cardinal 6.8mm SPC barrel that had the "improved" chamber. I used a Stag lefty upper and a stag lefty 6.8mm BCG. All 3 components were bought from separate places.

    So... How are you supposed to *use* HS gauges? Do I need to take the barrel out of the upper? Do I need to use the HS gauges with just the barrel & bolt, but no bolt carrier? Do I need to take the firing pin, extractor and ejector out of the bolt? Why do my HS gauges have this big slot cut into the bolt-facing end of the gauge? Do I need to try to align that slot with anything?

    And why couldnt i find any 6.8mm field HS gauges?

    My 2 manson 6.8mm headspace gauges didnt come with any instructions. Now on the manson site they had a blurb about some extra things you had to be careful of when measuring headspace on improved chambers. Im not sure if that situation applies to the 6.8mm improved system.
    http://www.mansonreamers.com/Instruc...y%20Gaging.pdf

  2. #2
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    Quote Originally Posted by opticalc View Post
    I built an upper with a kotonics/cardinal 6.8mm SPC barrel that had the "improved" chamber. I used a Stag lefty upper and a stag lefty 6.8mm BCG. All 3 components were bought from separate places.

    So... How are you supposed to *use* HS gauges? Do I need to take the barrel out of the upper? Do I need to use the HS gauges with just the barrel & bolt, but no bolt carrier? Do I need to take the firing pin, extractor and ejector out of the bolt? Why do my HS gauges have this big slot cut into the bolt-facing end of the gauge? Do I need to try to align that slot with anything?

    And why couldnt i find any 6.8mm field HS gauges?

    My 2 manson 6.8mm headspace gauges didnt come with any instructions. Now on the manson site they had a blurb about some extra things you had to be careful of when measuring headspace on improved chambers. Im not sure if that situation applies to the 6.8mm improved system.
    http://www.mansonreamers.com/Instruc...y%20Gaging.pdf
    Barrel can stay in the receiver. Generally on Go/No Go gauges, you just need to remove the Extractor spring and insert and then put the bolt back into the bolt carrier (do not re-install the firing pin or cam pin).
    Slide the BCG back into the receiver. The end of the bolt carrier should poke out the back of the receiver slightly. If it sits flush with the receiver, then you have a problem.



    C4

  3. #3
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    i've never removed the extractor when checking headspace although i'm willing to be educated...

  4. #4
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    I'll run it down the way it is in the TM and how it is done in the military.

    Insert charging handle, bolt assy. (that means complete), and bolt carrier into upper receiver.

    Insert headspace gage into chamber area.

    Press the rear of the bolt and carrier assy. and charging handle forward using light finger pressure into the chamber area.

    Bolt should not rotate into the locked position and the bolt carrier must protrude from the rear of the upper receiver assy. for proper headspace.

  5. #5
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    The bolt should lock up on the "go" gauge. it should not lock up on the "no-go" or "field" gauge.

    Most guys just use a "field" gauge with 5.56 chamber.

    I'm ignorant about your improved 6.8 chamber. I would call Manson and ask them directly about that chamber and their gauges.

  6. #6
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    If you're using the .223 Forster gauges (the whole set), many 5.56mm NATO chambered guns will close on a NO-GO but won't (and shouldn't) on a FIELD. I usually just use a USGI FIELD to make sure there isn't excessive headspace (the dangerous kind).
    Chief Armorer for Elite Shooting Sports in Manassas VA
    Chief Armorer for Corp Arms (FFL 07-08/SOT 02)

  7. #7
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    FWIW the Brownell's website has lots of good "how to" pages not just for this but for lots of other stuff.
    It is bad policy to fear the resentment of an enemy. -Ethan Allen

  8. #8
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    Quote Originally Posted by taliv View Post
    i've never removed the extractor when checking headspace although i'm willing to be educated...

    The reason is that can wear/damage the gauge.

    Just to be clear, you leave the extractor in, but remove the spring and insert.


    C4

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    Quote Originally Posted by gotm4 View Post
    If you're using the .223 Forster gauges (the whole set), many 5.56mm NATO chambered guns will close on a NO-GO but won't (and shouldn't) on a FIELD. I usually just use a USGI FIELD to make sure there isn't excessive headspace (the dangerous kind).
    Agree. I think people might be talking about a couple different things here (Go/No Go) and how to properly fit a bolt to a barrel following a set criteria by the manufacturer.

    For instance, Novekse has a set criteria for EACH of his barrel lengths. He has his own HS gauges that I am required to use on his barrels.



    C4

  10. #10
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    I guess I should mentioned that I only use a "Field" gage as well. Ooops...

    Quote Originally Posted by gotm4 View Post
    If you're using the .223 Forster gauges (the whole set), many 5.56mm NATO chambered guns will close on a NO-GO but won't (and shouldn't) on a FIELD. I usually just use a USGI FIELD to make sure there isn't excessive headspace (the dangerous kind).

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