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Thread: Loose gas key

  1. #31
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    When I build up a carrier and key, I like to start with a stripped BCM carrier. Used to be able to get them that way. Whoever they had as a supplier at one time had a really nice, smooth grey surface.

    Anyway, the carrier key is supposed to be made of a softer steel, but still has chrome lining in the bore where it telescopes over the gas tube. For a long time, many low rate companies sourced keys that were harder steel, without chrome lining.

    I modified my Brownell's staking tool so that the screw heads are rounded and not sharp points, to provide a better stake with less galling of the carrier key body.

    I strip the carrier and key of grease with a good cleaning, then acetone bathe them so they're bone dry. I like to rough texture the surfaces that will be joined so they take a sealant better, and I have used Red LT #271, but would also consider Rocksett as well. US made grade 8 fasteners, also degreased and acetone bathed with Red LT 271 and a torque driver finish the assembly. I usually test fit before using sealant to make sure the key is aligned with the gas tube aperture in the face of the upper.

    Once they are together, I use the staking tool to put the stakes in, and will re-phosphate the impinged areas. I know the TM doesn't call for sealant, but I prefer it.

    I also recommend against staking the key with impact. The tools like the MOACKS and the Brownell's use compression, which isn't going to knock the seal loose. The TM also has an interesting treatment for deformities on the carrier key mouth. There's a tool for re-forming that, using impact with a small brass hammer.

  2. #32
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    It's the tool at the bottom right.



    Quote Originally Posted by LRRPF52 View Post
    When I build up a carrier and key, I like to start with a stripped BCM carrier. Used to be able to get them that way. Whoever they had as a supplier at one time had a really nice, smooth grey surface.

    Anyway, the carrier key is supposed to be made of a softer steel, but still has chrome lining in the bore where it telescopes over the gas tube. For a long time, many low rate companies sourced keys that were harder steel, without chrome lining.

    I modified my Brownell's staking tool so that the screw heads are rounded and not sharp points, to provide a better stake with less galling of the carrier key body.

    I strip the carrier and key of grease with a good cleaning, then acetone bathe them so they're bone dry. I like to rough texture the surfaces that will be joined so they take a sealant better, and I have used Red LT #271, but would also consider Rocksett as well. US made grade 8 fasteners, also degreased and acetone bathed with Red LT 271 and a torque driver finish the assembly. I usually test fit before using sealant to make sure the key is aligned with the gas tube aperture in the face of the upper.

    Once they are together, I use the staking tool to put the stakes in, and will re-phosphate the impinged areas. I know the TM doesn't call for sealant, but I prefer it.

    I also recommend against staking the key with impact. The tools like the MOACKS and the Brownell's use compression, which isn't going to knock the seal loose. The TM also has an interesting treatment for deformities on the carrier key mouth. There's a tool for re-forming that, using impact with a small brass hammer.



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  3. #33
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    Do you have a link for that tool?

    Quote Originally Posted by Iraqgunz View Post
    It's the tool at the bottom right.


  4. #34
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    Unobtanium. That's from my collection.

    Quote Originally Posted by titsonritz View Post
    Do you have a link for that tool?



    Owner/Instructor at Semper Paratus Arms

    Facebook: https://www.facebook.com/SemperParatusArms/

    Semper Paratus Arms AR15 Armorer Course http://www.semperparatusarms.com/cou...-registration/

    M4C Misc. Training and Course Announcements- http://www.m4carbine.net/forumdisplay.php?f=141

    Master Armorer/R&D at SIONICS Weapon Systems- http://sionicsweaponsystems.com

  5. #35
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    Quote Originally Posted by titsonritz View Post
    Do you have a link for that tool?
    That tool is listed as Key, Machine, P/N 12926769, (NSN 5315-01-310-0370). It is part of the Direct Support/General Support Maintenance Kit for 5.56mm Rifle, M16 Series, P/N 8426685.

    Their are currently two sources of this tool for the Government, Howie Manufacturing Company of Camden, NJ and L.A. Martin Company of Dearborn, MI. If you really want one, try contacting either of these two places. Howie is a small concerns (less than $500,000 annual) might be more willing to work with you than LA Martin.

    Oh and as to the TM's "interesting treatment for deformities on the carrier key mouth", there is this immediately above the instructions:

    -CAUTION-
    Extreme care must be exercised during the following procedure to ensure that the striking force is not directed to the attaching screws [my emphasis] and that the tube portion is not enlarged or flared beyond original requirement. Such enlargement would permit loss of gas pressure when the key and gas tube come together during functioning. The edge of workbench is recommended.

    (I am currently trying to find drawings for many of these special tools.)
    Last edited by lysander; 10-15-15 at 08:43.

  6. #36
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    Quote Originally Posted by HansTheHobbit View Post
    Knowing BCM customer service, they'll probably fix it. If not, then just crank 'em back down. It's actually up for debate whether staking does much good or not. It certainly doesn't hurt, except that it's permanent, but as you have experienced it's entirely possible for even properly staked gas keys to come loose.
    Staking is absolutely necessary and not negotiable if you're going to shoot the gun much. If it's going to sit in the safe, then nothing matters. Those carrier key screws will come untorqued with shooting vibration and the heat there (~1700 degrees F) will cause any thread locker to let go. The only way to keep that from happening is to PROPERLY stake (look at a Colt BCG for reference) those screws.
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  7. #37
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    Quote Originally Posted by Wayne Dobbs View Post
    ...and the heat there (~1700 degrees F)...
    Nowhere near that hot.

    The gas temperature only gets to around 400 to 500 F (depending on how long your gas system is), and the gas doesn't stay around long enough to soak into the carrier.

    During extended full auto fire you might see 300 to 350 F in the bolt carrier.

    Still, it does get too hot for thread-locker type glue.

  8. #38
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    Quote Originally Posted by HansTheHobbit View Post
    Knowing BCM customer service, they'll probably fix it. If not, then just crank 'em back down. It's actually up for debate whether staking does much good or not. It certainly doesn't hurt, except that it's permanent, but as you have experienced it's entirely possible for even properly staked gas keys to come loose.
    A) it's not really up for debate
    B) it's not permanent

    Being that the gun was purchased used, there's no way to know if it had been messed with before. For all we know, the original owner used an adjustable gas key and swapped it back out before selling the gun. New gas key, new screws, clean thoroughly, reinstall with thread locker, stake it and go shoot.

  9. #39
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    Quote Originally Posted by lysander View Post
    Still, it does get too hot for thread-locker type glue.
    I really wish someone would do a test to prove if threadlocker alone could be a suitable alternative to staking. I have never seen a test to prove if it works or doesn't.

  10. #40
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    Quote Originally Posted by 556Cliff View Post
    I really wish someone would do a test to prove if threadlocker alone could be a suitable alternative to staking. I have never seen a test to prove if it works or doesn't.
    Considering that the TM calls for both, I'd assume it's already been tested.

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