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Thread: Can anyone help with this malfunction?

  1. #1
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    Can anyone help with this malfunction?

    I recently aquired a used Colt 6721. It came with an unshrouded firing pin type half moon carrier, blue extractor insert, carbine buffer and gas rings which allowed the bolt to collapse on itself. Since its a used gun and ammo is pretty much unobtainable I decided to try to do some maintenance before I took it to the range. I put in a new BCM buffer spring and H-Buffer, new BCM gas rings and a new BCM extractor sping, black insert and O-ring.

    I finally obtained some ammo and a few magazines so I tried to chamber a few rounds just to see how things were going and got some bad news.

    [IMG][/IMG]
    [IMG][/IMG]

    This happened only when hand cycling the action, never from a locked back bolt. It happened on one horrendous GI 30 round, one new old stock British 30 round and one brand new Colt 20 round. Occasionally it would completely fail for pick up a round from the magazine but I believe that may have only been from the old GI 30 round (I could be mistaken).

    I was careful to make sure I was pulling the charging handle all the way back and not riding it forward and it locked back on all the empty magazines so it does appear to be clearing the bolt catch and ammo in the magazine. Also, after changing the gas rings, if I rode the charging handle on the gun while empty the bolt would not fully go into battery but would once I pushed the charging handle the rest of the way forward.

    I tried removing the o-ring and nothing. I tried changing the gas rings back and it resolved the issue when riding the charging handle but I still experience the above malfunctions. I also switched back to the old buffer/spring and it seemed to experience less malfunctions, but they still occurred. The only thing I have not tried is going back to the old extractor spring/insert because I can't really see how that could be the problem, but who knows.

    In addition to changing those parts I also tried removing the firing pin because I read that the unshrouded firing pin can catch on the notch of the hammer and someone on TOS suggested that as a quick way to check, it is not. (For anyone who has not tried to work their action with no firing pin, DO NOT EVER DO THIS. I had to remove the receiver extension to seperate the receivers and get the bolt out.) I then tried the proper test and removed the hammer, this also did not solve the problem. Finally, I tried tightening the magazine catch one turn which also had no effect.

    So now I am at a loss. Any ideas? (Also the top image insists on being upside down for some reason, because that just seems to be my luck.)

  2. #2
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    Return the rifle to complete stock config and try again. If it functions as it should, upgrade one part at a time (don't know that you need the extractor O-ring) until you encounter the failure.
    Sticks

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    A person who is incapable of independent thought; a person who is herd animal-like in behavior; one who cannot distinguish between right and wrong; a foolish person.
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  3. #3
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    Thanks Sticks. I pretty much already did that except for the extractor spring/insert, but the rounds aren't getting anywhere close to the bolt face before getting hung up so I can't see how that would be the issue. The best results I had were going back to the original action spring/carbine weight buffer but this still wasn't perfect. I carry a 6920 at work and our carry condition is magazine inserted with an empty chamber. I've never had a single problem chambering a round with that. Also, if a brand new BCM action spring and H buffer don't work, doesn't it seem like there must be a deeper problem?

    This is another picture which depicts the bolt position when the problem occurs.
    [IMG][/IMG]

  4. #4
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    Have you taken a good hard look at the area where the feed ramps on the upper receiver and the barrel are? You said it is used, parts in the bolt carrier sound wore out, that means some wear and tear. Maybe the tip of the bullet is actually catching the end of the barrel. Maybe the upper has M4 type feed ramps and the barrel doesn't(some parts already replaced).
    “Never try to teach a pig to sing; it wastes your time and it annoys the pig.” Robert Heinlein

  5. #5
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    Quit hand cycling live rounds. It's not a safe method, and it tells you nothing about real world function.

    You really have to go shoot it to learn anything. Ammo is commonly scratched by the normal feeding in an AR.
    "You people have too much time on your hands." - scottryan

  6. #6
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    The feed ramps seem alright from what I can tell. Here's a picture. I learned how to post pictures so I'm going nuts with it.

    [IMG][/IMG]

  7. #7
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    Quote Originally Posted by markm View Post
    Quit hand cycling live rounds. It's not a safe method, and it tells you nothing about real world function.

    You really have to go shoot it to learn anything. Ammo is commonly scratched by the normal feeding in an AR.
    This... I can't count the number of scratched up rounds that I've scratched up. I usually throw them in the plinker pile. Sucks when they're expensive match grade rounds...

  8. #8
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    Quote Originally Posted by markm View Post
    Quit hand cycling live rounds. It's not a safe method, and it tells you nothing about real world function.

    You really have to go shoot it to learn anything. Ammo is commonly scratched by the normal feeding in an AR.
    This.

  9. #9
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    Guys, regarding the hand cycling, the original poster is saying that he can't even chamber the first round. That's a problem.

    The feed ramps look fine. You can ignore the extractor, extractor spring, inserts/o-ring, and gas rings for now.

    I'd focus on the magazines (which you already have done) and action spring(s). Is there a chance there is an issue with your buffer tube?

    Can you describe or link to what you did when you checked the relationship of your notched hammer/bolt carrier/firing pin? Feel free to PM or email me.

    Joe Mamma
    "Reliability above all else"
    NRA Certified Pistol and Rifle Instructor, Life Member
    Glock Certified Armorer
    Beretta & Sig Sauer Certified Pistol Armorer
    Colt Certified 1911 & AR-15/M16/M4 Law Enforcement Armorer

  10. #10
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    Also, just out of curiosity, try a different bolt carrier. If possible, try a different design like a full auto/fully shrouded bolt carrier.

    Joe Mamma
    "Reliability above all else"
    NRA Certified Pistol and Rifle Instructor, Life Member
    Glock Certified Armorer
    Beretta & Sig Sauer Certified Pistol Armorer
    Colt Certified 1911 & AR-15/M16/M4 Law Enforcement Armorer

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