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Thread: Teach me about Direct Impingement

  1. #21
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    Quote Originally Posted by MistWolf View Post

    A question- how does the gas get from the carrier key to the rings? Is the carrier key hollow all the way through?
    “A leader is best when people barely know he exists, when his work is done, his aim fulfilled, they will say: we did it ourselves.” -Lao Tzu


    http://quibphotography.com/

  2. #22
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    Now we need the pics showing the gas rings only have .071 end clearance when in the carrier. The huge gaps we are used to seeing don't exist when the bolt rings are compressed in place.

    It helps debunk the gas ring gap "danger" that doesn't exist - and why other knowledgeable shooters have insisted the AR will work just fine with one ring only.

    K.L. Davis's link is very informative and dovetails well with the slides from TACOM. He acknowledges that rotation of the bolt may be lifting the extractor, so the test by TACOM to spin the bolt with added weight is significant in that it couldn't achieve lift.

    Two forces act on the bolt - pressure from the case, and the DI directly on the back of the bolt. It's been said DI will actually help compensate for bolt loading by it's opposing force, allowing the bolt to turn more easily. If rotation isn't lifting the extractor, what is?

    Since headspacing means there is some slight movement of the bolt, could the sudden sequential opposing pressures be causing the extractor to rock on the pivot pin, creating lift? The pivot's attached to the bolt, and the bolt does move a few thousandths.

    Mount a bolt where two opposing pistons can jar it with 10k to 35k pounds and rattle it, I speculate high speed photography will show it rocking.

  3. #23
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    Quote Originally Posted by tirod View Post
    ...Two forces act on the bolt - pressure from the case, and the DI directly on the back of the bolt. It's been said DI will actually help compensate for bolt loading by it's opposing force, allowing the bolt to turn more easily...
    A brass cartridge expands from the pressure of the burning gunpowder and sticks to the walls. This helps reduce backthrust against the bolt face. When the pressure drops, the brass contracts. (Steel does not expand or contract as well as brass. This is why I do not use steel cased ammo in any of my wepaons.)

    Most bolts lock up with no play. Are ARs different?

  4. #24
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    Head space means there is some play.

  5. #25
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    Now Im confused and have a question. What happens on a piston gun like the 416 or ADC to the gases that go through the gas key and push forward on the bolt when there is no gas key or gases going into the bolt carrier? Dont piston guns use bolts with gas rings?

  6. #26
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    Quote Originally Posted by crossgun View Post
    Now Im confused and have a question. What happens on a piston gun like the 416 or ADC to the gases that go through the gas key and push forward on the bolt when there is no gas key or gases going into the bolt carrier? Dont piston guns use bolts with gas rings?
    There is no gas transfer into the BCG, therefore significantly more force is exerted on the locking lugs and lugs in the barrel extension than with the gas system the gun is designed to work with.

    ARs with shoe-horned piston systems do not require the bolt to have gas-rings, though some do to properly align the bolt within the BCG.
    Jack Leuba
    Director, Military and Government Sales
    Knight's Armament Company
    jleuba@knightarmco.com

  7. #27
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    Deleted. See below. Site is acting strange.
    Last edited by Quib; 07-02-10 at 07:47.
    “A leader is best when people barely know he exists, when his work is done, his aim fulfilled, they will say: we did it ourselves.” -Lao Tzu


    http://quibphotography.com/

  8. #28
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    Quote Originally Posted by tirod View Post
    Now we need the pics showing the gas rings only have .071 end clearance when in the carrier. The huge gaps we are used to seeing don't exist when the bolt rings are compressed in place.










    “A leader is best when people barely know he exists, when his work is done, his aim fulfilled, they will say: we did it ourselves.” -Lao Tzu


    http://quibphotography.com/

  9. #29
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    Well, I obviously transposed the numbers. .017, right. Even better.

    And a further question (I never thought to ask) is whether gas opens the port cover, or bolt movement:


    http://www.ar15.com/forums/topic.htm...f=118&t=503005

    I would have thought bolt carrier movement opened the port cover, but, well, read up for yourself.

  10. #30
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    LOL……I saw that thread.

    I’m going to venture to say that the ejection port cover opening is based solely off mechanical action verses gas pressure.

    I do not have hard data to back this up, but I’m guessing that after the energy is expended from the gas impulse of firing the rifle, that little energy is left in the form of pressure exiting the gas vents in an amount large enough to “blow open” the ejection port door.

    If this was truly the case, that gas pressure alone acted to open the ejection port door, would we not eventually see gas erosion pitting on the inner surface of the door?

    The gas pressure enters the carrier key where it is dumped into a piston chamber. The opening into the carrier (piston chamber) acts as a venturi. And we know that with a venturi, an increase in velocity, equals a decrease in pressure. The pressure remaining from the gas impulse has its energy robbed in the form of work expelled to move the piston (bolt). Therefore, little pressure is remaining in the form of exhaust gasses ported overboard.

    This is my take on it. If I’m wrong, I stand corrected.
    “A leader is best when people barely know he exists, when his work is done, his aim fulfilled, they will say: we did it ourselves.” -Lao Tzu


    http://quibphotography.com/

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