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Thread: Stubborn barrel nut

  1. #1
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    Stubborn barrel nut

    A buddy of mine came by tonight with a new upper receiver that he wanted to reconfigure. It was from a reputable manufacturer and originally came with an FSB, standard barrel nut etc. My friend wanted to remove the FSB, install a low profile gas block and a Troy rail. Simple, right?

    Well, the FSB comes off, no problem. I then ran into serious trouble with the barrel nut. Using a cheater bar, I was initially unable to move it at all. Finally, it moved slightly and then stopped dead. We worked on it for almost an hour, taking our time and being very careful trying not to damage anything. Right before I gave up, I decided to try and torque it back down to see if we could get the nut moving. Applying torque clockwise, the nut moved slightly. I then reversed the torque counterclockwise and it finally loosened. It was tightened well beyond 80 ft lbs and required a tremendous amount of torque to loosen.

    As you can imagine, the upper was slightly damaged. By slightly, I mean that the notch was slightly wallowed out. No cracking or visible shearing, just very slightly widened. Upon reassembly, the barrel was shifting as the barrel nut was torqued on. It looked Ok, with the feed ramps only slightly off center. It was able to shift due to the now widened notch in the upper.

    Everything looked fine until I dropped a BCG into the upper. We tried three in all, 2 BCM's and a WMD bcg. The WMD would not go into battery. One BCM closed easily and the second BCM closed with a little resistance. The lugs of the the WMD bcg were slightly larger than the BCM's and were contacting the extension. It was unable to go into battery because the extension / barrel were turned slightly in the upper. The combination of slightly larger bolt lugs (measured at 0.103) and the tilted extension would not allow the bolt to go into battery. The WMD bolt worked fine before disassembly.

    So, I have two questions:

    1) How can one remove an overly tight barrel nut without damaging the receiver? Or is it sometimes unavoidable?

    2) Should the upper be replaced under warranty due to the barrel nut being installed with more than 80 ft lbs of torque and causing unavoidable damage in order to remove it?

  2. #2
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    Just curious. What method were you using to secure the upper?

    You never know until you ask in regards to getting a replacement upper when you are doing the work yourself.

  3. #3
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    to answer questions,

    #1. try applying heat such as a torch next time around the barrel nut and threads, this has worked for me in the past. As far as the damage goes I have destroyed some barrel nuts in my day but have yet to widen the upper, were you using vice blocks?

    #2. Good luck with that one, just because you say they over torqued the barrel nut does not mean they will believe you and now you have no proof other than a messed up upper, how do they know you are not some jack ass screwing around where you should not be. It sucks but you may need to spring for another upper, and just use this one as a learning experience.
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  4. #4
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    When I have them that tight, I use a Dremel and cut them off and then pop the FSB and replace it. Simply because of the risk of damage as you saw.

    I doubt that they will warrantee this because you won't be able to prove it was overtorqued or they will say that you voided the warranty by wrenching on it.

    Quote Originally Posted by mtdawg169 View Post
    A buddy of mine came by tonight with a new upper receiver that he wanted to reconfigure. It was from a reputable manufacturer and originally came with an FSB, standard barrel nut etc. My friend wanted to remove the FSB, install a low profile gas block and a Troy rail. Simple, right?

    Well, the FSB comes off, no problem. I then ran into serious trouble with the barrel nut. Using a cheater bar, I was initially unable to move it at all. Finally, it moved slightly and then stopped dead. We worked on it for almost an hour, taking our time and being very careful trying not to damage anything. Right before I gave up, I decided to try and torque it back down to see if we could get the nut moving. Applying torque clockwise, the nut moved slightly. I then reversed the torque counterclockwise and it finally loosened. It was tightened well beyond 80 ft lbs and required a tremendous amount of torque to loosen.

    As you can imagine, the upper was slightly damaged. By slightly, I mean that the notch was slightly wallowed out. No cracking or visible shearing, just very slightly widened. Upon reassembly, the barrel was shifting as the barrel nut was torqued on. It looked Ok, with the feed ramps only slightly off center. It was able to shift due to the now widened notch in the upper.

    Everything looked fine until I dropped a BCG into the upper. We tried three in all, 2 BCM's and a WMD bcg. The WMD would not go into battery. One BCM closed easily and the second BCM closed with a little resistance. The lugs of the the WMD bcg were slightly larger than the BCM's and were contacting the extension. It was unable to go into battery because the extension / barrel were turned slightly in the upper. The combination of slightly larger bolt lugs (measured at 0.103) and the tilted extension would not allow the bolt to go into battery. The WMD bolt worked fine before disassembly.

    So, I have two questions:

    1) How can one remove an overly tight barrel nut without damaging the receiver? Or is it sometimes unavoidable?

    2) Should the upper be replaced under warranty due to the barrel nut being installed with more than 80 ft lbs of torque and causing unavoidable damage in order to remove it?



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  5. #5
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    80 pounds of installation torque does not equal 80 pounds of removal torque. In any sliding system there are two types of friction. Static friction and dynamic friction. During the torquing process the stressing of the fastener is the desired outcome but the sliding component of the male and female threads must also be accounted for. To make a part move in a sliding system static friction must first be overcome. The force required to get the part moving is greater than the force required to keep it moving. Torqued fasteners are no different. 80 pounds of installation torque was measured during the dynamic friction phase. Removal of the same fastener will require greater than 80 pounds of force as the static friction must first be overcome. This is why force required to remove is no measure of the force that was used to install. One way to measure how much force was used to install a fastener is to witness one part to the other, remove the part, then determine the torque required to return the parts to the same orientation. Of course this would require that neither part was damaged during disassembly.

  6. #6
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    Re: Stubborn barrel nut

    Quote Originally Posted by AKDoug View Post
    Just curious. What method were you using to secure the upper?

    You never know until you ask in regards to getting a replacement upper when you are doing the work yourself.






    Quote Originally Posted by JR TACTICAL View Post
    to answer questions,

    #1. try applying heat such as a torch next time around the barrel nut and threads, this has worked for me in the past. As far as the damage goes I have destroyed some barrel nuts in my day but have yet to widen the upper, were you using vice blocks?

    #2. Good luck with that one, just because you say they over torqued the barrel nut does not mean they will believe you and now you have no proof other than a messed up upper, how do they know you are not some jack ass screwing around where you should not be. It sucks but you may need to spring for another upper, and just use this one as a learning experience.
    I tried both a Geisselle reaction rod and vice blocks. It was twisting inside the vise block and couldn't be removed without the GRR.

    I've never seen a barrel nut this tight before. I could literally put all my weight into it and it wouldn't budge.

  7. #7
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    Re: Stubborn barrel nut

    Quote Originally Posted by Iraqgunz View Post
    When I have them that tight, I use a Dremel and cut them off and then pop the FSB and replace it. Simply because of the risk of damage as you saw.

    I doubt that they will warrantee this because you won't be able to prove it was overtorqued or they will say that you voided the warranty by wrenching on it.
    Thanks IG. I wish I had thought of cutting it off last night.

  8. #8
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    Never mind
    Last edited by Hmac; 07-02-13 at 06:55.

  9. #9
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    Re: Stubborn barrel nut

    Quote Originally Posted by Tzed250 View Post
    80 pounds of installation torque does not equal 80 pounds of removal torque. In any sliding system there are two types of friction. Static friction and dynamic friction. During the torquing process the stressing of the fastener is the desired outcome but the sliding component of the male and female threads must also be accounted for. To make a part move in a sliding system static friction must first be overcome. The force required to get the part moving is greater than the force required to keep it moving. Torqued fasteners are no different. 80 pounds of installation torque was measured during the dynamic friction phase. Removal of the same fastener will require greater than 80 pounds of force as the static friction must first be overcome. This is why force required to remove is no measure of the force that was used to install. One way to measure how much force was used to install a fastener is to witness one part to the other, remove the part, then determine the torque required to return the parts to the same orientation. Of course this would require that neither part was damaged during disassembly.
    I'm aware that it will take more torque to remove than to install. However, in this case, I was was able to reinstall the nut with 45 lbs, get good gas tube alignment and easily remove it. The amount of torque used during assembly wasn't necessary to get alignment and was WAY over the max spec of 80. My torque wrench maxes out at 120. The nut required more than that to be removed, much more.

    So far it sounds like cutting one off is the best option.

  10. #10
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    Gunz, can you give us some detail on how you cut a barrel nut off without cutting into the upper?
    B.A.S. Mechanical Engineering Technology

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