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Thread: Bolt Failure Questions

  1. #11
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    Lots of factors to consider in my opinion. Firing schedule, rate of fire, and lubrication.

    I have a BCM bolt that has about 10K on it and at least 40% of those rounds were suppressed.

    I also keep my weapon lubed very wet and I don't do silly magazine dumps. Thus far I have only replaced the ejector spring. The gas rings and extractor spring are original.

    As for carriers the failures usually are attributed to faulty staking of the carrier key. Also getting primers or anvils inside the carrier key and being unable to remove them which will require re-keying.



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  2. #12
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    Quote Originally Posted by Traveshamockery View Post
    Why is the 7 lug pattern more common nowadays?
    It's not really that common. The majority of rifle designs with a rotating bolt use two large locking lugs, some three. More than that is actually rare. One reason the AR uses multiple locking lugs is to reduce the amount of rotation needed when the bolt locks and unlocks. Smaller lugs means less movement is needed and seven lugs is stronger than two lugs of the same size
    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"

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  3. #13
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    Quote Originally Posted by MistWolf View Post
    It's not really that common. The majority of rifle designs with a rotating bolt use two large locking lugs, some three. More than that is actually rare. One reason the AR uses multiple locking lugs is to reduce the amount of rotation needed when the bolt locks and unlocks. Smaller lugs means less movement is needed and seven lugs is stronger than two lugs of the same size
    you sure? there are numerous small arms that use 6-7 lugs, L85, AUG, M4, SCAR, ACR, ARX-160, HK416(though this is just a piston AR), the list can go on.
    Quote Originally Posted by C4IGrant View Post
    Colt builds War Horses, not show ponies.
    Quote Originally Posted by Iraqgunz View Post
    This is 2012. The world is going to end this December and people are still trying to debate the merits of piece of shit, cost cutting crap AR's. Really?

  4. #14
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    Quote Originally Posted by Traveshamockery View Post
    Why is the 7 lug pattern more common nowadays?
    From a design standpoint... less rotation to lock/unlock.

    The AR-15 bolt requires 22.5 degrees of rotation, versus 60 or more with some other designs.
    Please let me know if I have offended you...
    I would like to move on to my next task.


    I provide legal consultation and training - specializing in the Law of Gravity.

  5. #15
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    Quote Originally Posted by sinlessorrow View Post
    you sure? there are numerous small arms that use 6-7 lugs, L85, AUG, M4, SCAR, ACR, ARX-160, HK416(though this is just a piston AR), the list can go on.
    That list is longer than I realized but still, the list of two lug rifles is even longer- Remington Models 721, 700 and variants, Winchester Model 70, Ruger M77, Mauser Models 91, 93 & 98, SMLE and nearly every other bolt action, Garand, M1 Carbine, M14 and so on. Now that I think about it, the list of three lug designs may be rather short.

    The Remington 788 used a multi lug bolt and had a bolt lift of only 60 degrees. It was supposed to be that it was difficult to get all the lugs to bear evenly when locked up. Didn't seem to be a problem with the 788, however
    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

  6. #16
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    Quote Originally Posted by MistWolf View Post
    It's not really that common. The majority of rifle designs with a rotating bolt use two large locking lugs, some three. More than that is actually rare. One reason the AR uses multiple locking lugs is to reduce the amount of rotation needed when the bolt locks and unlocks. Smaller lugs means less movement is needed and seven lugs is stronger than two lugs of the same size
    Quote Originally Posted by K.L. Davis View Post
    From a design standpoint... less rotation to lock/unlock.

    The AR-15 bolt requires 22.5 degrees of rotation, versus 60 or more with some other designs.
    Thanks to you both for the good answers.
    This isn't an illegal gun, it's an "undocumented protection device". Don't be so insensitive.

  7. #17
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    Quote Originally Posted by MistWolf View Post
    That list is longer than I realized but still, the list of two lug rifles is even longer- Remington Models 721, 700 and variants, Winchester Model 70, Ruger M77, Mauser Models 91, 93 & 98, SMLE and nearly every other bolt action, Garand, M1 Carbine, M14 and so on. Now that I think about it, the list of three lug designs may be rather short.

    The Remington 788 used a multi lug bolt and had a bolt lift of only 60 degrees. It was supposed to be that it was difficult to get all the lugs to bear evenly when locked up. Didn't seem to be a problem with the 788, however

    And old, there are more modern auto loading rifles with 6-7 lug bolts.
    Last edited by sinlessorrow; 09-11-12 at 13:07.
    Quote Originally Posted by C4IGrant View Post
    Colt builds War Horses, not show ponies.
    Quote Originally Posted by Iraqgunz View Post
    This is 2012. The world is going to end this December and people are still trying to debate the merits of piece of shit, cost cutting crap AR's. Really?

  8. #18
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    lugs

    The AR bolt is one of the most used parts on modern designs so it is pretty good, Stoner made the lugs larger when they developed the Stoner 63 largely because they couldn't get Carpenter 151,

    It's easy to see that when you have more lugs you can have shorter lugs, shorter lugs on bolt and barrel extension means that you are going to have a more "reliable" feed.

    If you had 2 lugs, that are .375 in length not width, and the barrel extension matches the .375 length, then you have to drive a cartridge 0.75 inches past the end of the magazine before the tip is stabilized into the chamber.

  9. #19
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    Quote Originally Posted by halmbarte View Post
    Both of the locking lugs on either side of the extractor take more stress than the other lugs, so they tend to crack and fail.
    They do not take more stress. They are weaker because they are undercut by the extractor grove.

    Quote Originally Posted by Traveshamockery View Post
    Why is the 7 lug pattern more common nowadays?
    Technically, it's an 8 lug pattern with one missing (extractor grove).

    360 / 8 = 45, 45 / 2 = 22.5 Degrees

    Quote Originally Posted by K.L. Davis View Post
    From a design standpoint... less rotation to lock/unlock.

    The AR-15 bolt requires 22.5 degrees of rotation, versus 60 or more with some other designs.
    Yep... It's all about the timing. Fewer lugs would require a larger volume of gas for a longer period of time to unlock the bolt.
    Last edited by MarkG; 09-12-12 at 10:16.

  10. #20
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    Wow. This thread is awesome. I didn't know almost any of that.
    We miss you, AC.
    We miss you, ToddG.

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