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Thread: A bit of help with this malfunction.

  1. #21
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    Quote Originally Posted by MK18Pilot View Post
    The spring in a magazine is under a constant load. As a cartridge is stripped from the magazine and chambered, the next cartridge in the stack is moved up in the magazine and is trapped by the feed lip well before the chambered cartridge can be fired. That is to say that it is "on deck" before the recoil phase of operation begins.

    If the bolt is in battery I think the carrier is holding the cartridges down off of the feed lips. As soon as the bottom of the carrier clears the rear of the case in the recoil stroke the cartridge is ready for feeding in the battery stroke.

  2. #22
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    Quote Originally Posted by Tweak View Post
    If the bolt is in battery I think the carrier is holding the cartridges down off of the feed lips. As soon as the bottom of the carrier clears the rear of the case in the recoil stroke the cartridge is ready for feeding in the battery stroke.
    You are correct. The cocking surface of the bolt carrier keeps the cartridge stack depressed and tension off of the feed lips. Even then, there is no way the bolt group can "outrun" the magazine. Now we need to find out what the distance between the on deck cartridge and feed lip is...

  3. #23
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    A good approximation would be half a cartridge base diameter.

    And yes, check the carrier key for leakage, then re-test with full-5.56 ammo such as XM193.

    If there is no leak, and the XM-193 works the rifle, then you're back to the "doctor, doctor" joke. The rifle is telling you "don't feed me that."

  4. #24
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    The bolt pushes the cartridge in the mag down approximately 1/8 inch.

    Mk18Pilot, how do you figure it's impossible for the bolt to out run the magazine?
    INSIDE PLAN OF BOX
    1. ROAD-RUNNER LIFTS GLASS OF WATER- PULLING UP MATCH
    2. MATCH SCRATCHES ON MATCH-BOX
    3. MATCH LIGHTS FUSE TO TNT
    4. BOOM!
    5. HA-HA!!

    -WILE E. COYOTE, AUTHOR OF "EVERYTHING I NEEDED TO KNOW IN LIFE, I LEARNED FROM GOLDBERG & MURPHY"

    http://i115.photobucket.com/albums/n289/SgtSongDog/AR%20Carbine/DSC_0114.jpg
    I am American

  5. #25
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    Quote Originally Posted by MistWolf View Post
    The bolt pushes the cartridge in the mag down approximately 1/8 inch.

    Mk18Pilot, how do you figure it's impossible for the bolt to out run the magazine?
    The spring exerts constant pressure on the cartridge stack. There is just no way the stack is going to pause long enough to allow the bolt group to complete the recoil phase and get half way through counter-recoil before it tries to move upward.

  6. #26
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    I'm not sure I'm tracking you. The cartridge cannot rise in the magazine until the bolt clears the rim in it's rearward motion
    INSIDE PLAN OF BOX
    1. ROAD-RUNNER LIFTS GLASS OF WATER- PULLING UP MATCH
    2. MATCH SCRATCHES ON MATCH-BOX
    3. MATCH LIGHTS FUSE TO TNT
    4. BOOM!
    5. HA-HA!!

    -WILE E. COYOTE, AUTHOR OF "EVERYTHING I NEEDED TO KNOW IN LIFE, I LEARNED FROM GOLDBERG & MURPHY"

    http://i115.photobucket.com/albums/n289/SgtSongDog/AR%20Carbine/DSC_0114.jpg
    I am American

  7. #27
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    Quote Originally Posted by MistWolf View Post
    I'm not sure I'm tracking you. The cartridge cannot rise in the magazine until the bolt clears the rim in it's rearward motion
    For the bolt to outrun the magazine, the cartridge stack would have to fight spring tension and hold its position 1/8 inch below the feed lips during counter recoil.

  8. #28
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    Ok, I'm following you there. A few questions remain-

    How long does it take before the spring begin accelerating the stack into proper position? How fast does the spring relax? Will a weaker magazine spring increase the time it takes to accelerate the stack into place?

    How long is the time between the bolt clearing the rim in the stack until it returns to begin stripping the cartridge from the magazine? How much does that time change with a change in bolt speed?

    How much does the violence of the higher bolt speed affect the positioning of the stack in the magazine? Will a weaker spring allow the stack to be displaced during the bolt cycle?
    INSIDE PLAN OF BOX
    1. ROAD-RUNNER LIFTS GLASS OF WATER- PULLING UP MATCH
    2. MATCH SCRATCHES ON MATCH-BOX
    3. MATCH LIGHTS FUSE TO TNT
    4. BOOM!
    5. HA-HA!!

    -WILE E. COYOTE, AUTHOR OF "EVERYTHING I NEEDED TO KNOW IN LIFE, I LEARNED FROM GOLDBERG & MURPHY"

    http://i115.photobucket.com/albums/n289/SgtSongDog/AR%20Carbine/DSC_0114.jpg
    I am American

  9. #29
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    Quote Originally Posted by MistWolf View Post
    Ok, I'm following you there. A few questions remain-

    How long does it take before the spring begin accelerating the stack into proper position? How fast does the spring relax? Will a weaker magazine spring increase the time it takes to accelerate the stack into place?

    How long is the time between the bolt clearing the rim in the stack until it returns to begin stripping the cartridge from the magazine? How much does that time change with a change in bolt speed?

    How much does the violence of the higher bolt speed affect the positioning of the stack in the magazine? Will a weaker spring allow the stack to be displaced during the bolt cycle?
    Are you talking about "bounce" inside the mag?

    Another thing that might be considered is that with GI Issue 20 rd mags it is easier for the feed lips to get bent either up or down.

  10. #30
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    Quote Originally Posted by MistWolf View Post
    How long is the time between the bolt clearing the rim in the stack until it returns to begin stripping the cartridge from the magazine?
    We can figure the distance the bolt travels. Is there any way to convert RPM to bolt speed?

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