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Thread: Colt 6933 chokes on PMC bronze

  1. #11
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    Don't let it fool ya, jpaul. It's not the ammo. Put that Colt spring back in there
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  2. #12
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    Mistwolf,

    Your explanation is how I understood the interaction between the bolt face, ejector, extractor, & cartridge / spent case. My question is in regard to number 4. You specifically mention weak extractor spring. What about the opposite end of the spectrum? Let's presume the green extractor spring provided too much tension between the extractor, case rim, & ejector?

    I'm not asking because I'm married to my beloved green spring. I'm asking because it is noticably stronger than the Colt spring. It's apparent when installing the extractor to the bolt, & when fitting a dummy round under the extractor claw. I seem to remember the possibility of too much extractor tension a few years ago pertaining to midlength gas systems and using an o-ring w/ the updated / stronger extractor spring.

    Anyway, I'm curious to hear your or anyone elses thoughts on the matter.

    Quote Originally Posted by MistWolf View Post
    Don't let it fool ya, jpaul. It's not the ammo. Put that Colt spring back in there

    The Colt spring is installed.

  3. #13
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    If the spring pressure is too high, the extractor claw may not reliably snap over the rim of the case during chambering.

    I'm not certain, but too much spring pressure may also prevent the claw from releasing the case rim properly for ejection
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  4. #14
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    Great explanation.

    I had never considered the possibility of bore pressure assisting with extraction. Seems so obvious now. Thanks.

  5. #15
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    Quote Originally Posted by MistWolf View Post
    I'll try to explain why it's an extractor issue, step by step.

    1) The ejector is a spring loaded plunger. It presses the case outward until the front of the case clears the front of the ejection port. Therefore, as the case is being extracted, it's making contact with the rifle at three points. The ejector plunger, the extractor and the right side of the receiver. These three points hold the case in place as it's being dragged out of the chamber until it clears the front portion of the ejection port and is flung clear of the action by the ejector.

    2) A fresh round cannot be stripped from the magazine until the bolt face travels far enough to the rear that it clears the rim of the case. The bolt will not push a case from the magazine by pushing on the body of the case. It MUST catch the rim. You can test this for yourself by loading a magazine and working the charging handle. Pull the charging back to any point before the bolt would catch the rim and let it fly forward. It won't push the round out of the chamber. Here, I will insert the standard issue safety warning about testing the action with live ammo. Make up a few dummy rounds made from brass cases to perform this test.

    3) An empty case will eject long before the bolt travels far enough to pick up the next round. Therefore, it's possible for an AR to short stroke and eject a round at a point where the bolt will not strip a fresh round from the magazine. This can be tested by chambering an empty, loading a magazine with dummy rounds, then pulling back the charging handle just to the point where the empty is ejected. Once the empty is ejected, let the charging handle fly forward. The dummy round will not be pushed from the magazine. NOTE: Inserting an empty case in the chamber will result in the case getting stuck in the chamber. If you decide to perform this test, only use an unfired or a properly resized case.

    4) The case must be held against the ejector plunger in order for the ejector plunger to fling the case from the action. In a properly functioning rifle, the case is held by the extractor claw. The extractor claw is held in place by spring pressure. If the spring pressure is weak, the claw can slip over the rim and lose control of the case during extraction.

    5) The magazine can do nothing that causes the the case to be knocked loose from the extractor during extraction. The only way the magazine could cause problems with extraction/ejection is if the top round were to knock the extracting case loose from the extractor before ejection can occur. However, the top round is held down by the bolt & carrier until the bolt clears the rim. Long before the bolt clears the rim of the top round, the empty case will be ejected. Therefore, the magazine cannot cause extraction/ejection malfunctions.

    6) The malfunction we are discussing is not a double feed. A double feed is when two live rounds are fed from the magazine at the same time. A double feed is always a magazine issue. However, what we are seeing here is a live round and an empty being jammed in the action. Therefore, the cause is due to an empty case being left in the cation.

    Let's put all of this together and see what's happening. The empty isn't being ejected because the the extractor loses control of the case before the case can be ejected by the ejector.

    The case, having been released prematurely by the extractor, now lies in the action. The carrier continues to the rear, enough that the bolt clears the rim of the top round in the magazine. On its return, the bolt catches the rim of the top round to strip it from the magazine, but it is blocked before it can be fed into the chamber.

    If the empty case failed to eject due to short stroking, the carrier would not have traveled rearward enough for the mouth of the case to clear the ejection port and therefore would not be able to strip the top round from the magazine. If short stroking resulted in ejection without enough rearward travel of the carrier for the bolt to clear the rim of the top round, the carrier group would simply close on an empty chamber, or simply not go into battery on an empty chamber. We can eliminate short stroking as the cause of this malfunction.

    If the rifle were suffering from weak ejection, the ejector would push the case outward and the top round would normally push the empty out of the way. This could result in the top round being partially stripped from the magazine as the empty can impede the feeding of the fresh round as the empty is being knocked clear of the ejection port by the top round. It can also result in last round stove pipes. We can almost certainly eliminate weak ejection as the cause of this malfunction.

    Pressure in the bore helps press the case against the ejector plunger during extraction. As a suppressor keeps the pressure in the bore from dropping as quick, the pressure in the bore during extraction will be higher. This will improve extraction, but only serves to hide the fact that the extractor spring is weak and needs to be replaced. Once a spring begins failing, it continues to fail with each cycle and it's just a matter of time before it fails completely. The frequency of leaving extracted cases in the action will continue and soon the extractor will start leaving empties in the chamber.

    Over gassing will not cause a good extractor and a good extractor spring to lose control of the fired case. What it will do is overload a spring that has started to fail. A good extractor and spring will tear the rim off a stuck case before it will jump the rim and let go of it. While over gassing will expose the problem, over gassing isn't the cause.

    I hope this explains why this malfunction is an extraction issue, not short stroking, a magazine issue or over gassing
    I'm short on time now, as I have some other obligations to fill, but this is not a 100% to reference to extractor function.

  6. #16
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    Not to make a tangent to the OP question, but what do we really want the extractor to do? There are a few functions we can look at later.

  7. #17
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    Nice, detailed description

    Quote Originally Posted by MistWolf View Post
    I'll try to explain why it's an extractor issue, step by step.

    1) The ejector is a spring loaded plunger. It presses the case outward until the front of the case clears the front of the ejection port. Therefore, as the case is being extracted, it's making contact with the rifle at three points. The ejector plunger, the extractor and the right side of the receiver. These three points hold the case in place as it's being dragged out of the chamber until it clears the front portion of the ejection port and is flung clear of the action by the ejector.

    2) A fresh round cannot be stripped from the magazine until the bolt face travels far enough to the rear that it clears the rim of the case. The bolt will not push a case from the magazine by pushing on the body of the case. It MUST catch the rim. You can test this for yourself by loading a magazine and working the charging handle. Pull the charging back to any point before the bolt would catch the rim and let it fly forward. It won't push the round out of the chamber. Here, I will insert the standard issue safety warning about testing the action with live ammo. Make up a few dummy rounds made from brass cases to perform this test.

    3) An empty case will eject long before the bolt travels far enough to pick up the next round. Therefore, it's possible for an AR to short stroke and eject a round at a point where the bolt will not strip a fresh round from the magazine. This can be tested by chambering an empty, loading a magazine with dummy rounds, then pulling back the charging handle just to the point where the empty is ejected. Once the empty is ejected, let the charging handle fly forward. The dummy round will not be pushed from the magazine. NOTE: Inserting an empty case in the chamber will result in the case getting stuck in the chamber. If you decide to perform this test, only use an unfired or a properly resized case.

    4) The case must be held against the ejector plunger in order for the ejector plunger to fling the case from the action. In a properly functioning rifle, the case is held by the extractor claw. The extractor claw is held in place by spring pressure. If the spring pressure is weak, the claw can slip over the rim and lose control of the case during extraction.

    5) The magazine can do nothing that causes the the case to be knocked loose from the extractor during extraction. The only way the magazine could cause problems with extraction/ejection is if the top round were to knock the extracting case loose from the extractor before ejection can occur. However, the top round is held down by the bolt & carrier until the bolt clears the rim. Long before the bolt clears the rim of the top round, the empty case will be ejected. Therefore, the magazine cannot cause extraction/ejection malfunctions.

    6) The malfunction we are discussing is not a double feed. A double feed is when two live rounds are fed from the magazine at the same time. A double feed is always a magazine issue. However, what we are seeing here is a live round and an empty being jammed in the action. Therefore, the cause is due to an empty case being left in the cation.

    Let's put all of this together and see what's happening. The empty isn't being ejected because the the extractor loses control of the case before the case can be ejected by the ejector.

    The case, having been released prematurely by the extractor, now lies in the action. The carrier continues to the rear, enough that the bolt clears the rim of the top round in the magazine. On its return, the bolt catches the rim of the top round to strip it from the magazine, but it is blocked before it can be fed into the chamber.

    If the empty case failed to eject due to short stroking, the carrier would not have traveled rearward enough for the mouth of the case to clear the ejection port and therefore would not be able to strip the top round from the magazine. If short stroking resulted in ejection without enough rearward travel of the carrier for the bolt to clear the rim of the top round, the carrier group would simply close on an empty chamber, or simply not go into battery on an empty chamber. We can eliminate short stroking as the cause of this malfunction.

    If the rifle were suffering from weak ejection, the ejector would push the case outward and the top round would normally push the empty out of the way. This could result in the top round being partially stripped from the magazine as the empty can impede the feeding of the fresh round as the empty is being knocked clear of the ejection port by the top round. It can also result in last round stove pipes. We can almost certainly eliminate weak ejection as the cause of this malfunction.

    Pressure in the bore helps press the case against the ejector plunger during extraction. As a suppressor keeps the pressure in the bore from dropping as quick, the pressure in the bore during extraction will be higher. This will improve extraction, but only serves to hide the fact that the extractor spring is weak and needs to be replaced. Once a spring begins failing, it continues to fail with each cycle and it's just a matter of time before it fails completely. The frequency of leaving extracted cases in the action will continue and soon the extractor will start leaving empties in the chamber.

    Over gassing will not cause a good extractor and a good extractor spring to lose control of the fired case. What it will do is overload a spring that has started to fail. A good extractor and spring will tear the rim off a stuck case before it will jump the rim and let go of it. While over gassing will expose the problem, over gassing isn't the cause.

    I hope this explains why this malfunction is an extraction issue, not short stroking, a magazine issue or over gassing
    ETC (SW/AW), USN (1998-2008)
    CVN-65, USS Enterprise

  8. #18
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    Bore pressure most certainly aids extraction.

    We did some tests a while back firing various configurations with the extractor completely removed from the bolt.

    Most examples left the fired case in the chamber, which could be easily picked out afterwards.

    But some configurations actually popped the case right out and left it sitting on top of the magazine.


    Quote Originally Posted by mig1nc View Post
    Great explanation.

    I had never considered the possibility of bore pressure assisting with extraction. Seems so obvious now. Thanks.
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  9. #19
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    I agree, depending on the timing of events, some situations do come up when the extractor tensions for actual extraction from the chamber are minimal. In those situations, the extractor acts mostly as a fulcrum for proper ejection. Even when the extraction requires higher forces, the extractor still needs to act as a proper fulcrum for proper ejection. Extraction and ejection work within a balance of each other for operation as a whole.

  10. #20
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    Quote Originally Posted by tom12.7 View Post
    I agree, depending on the timing of events, some situations do come up when the extractor tensions for actual extraction from the chamber are minimal. In those situations, the extractor acts mostly as a fulcrum for proper ejection. Even when the extraction requires higher forces, the extractor still needs to act as a proper fulcrum for proper ejection. Extraction and ejection work within a balance of each other for operation as a whole.
    So Im curious. How big is a factor of friction on the extractor claw in grabbing the case? Ive noticed on NP3 or even nitrided bolts the extractor and ejector were always phosphated with the mfg stating having those parts too slick is a bad thing.

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