Page 1 of 2 12 LastLast
Results 1 to 10 of 15

Thread: AR10 bolt material

  1. #1
    Join Date
    Jan 2013
    Posts
    77
    Feedback Score
    1 (100%)

    AR10 bolt material

    i am thinking of doing an AR10 SBR build. i am looking at bolts and they all seem to be the "lesser" 9310 material unlike the desired c-158 for 5.56. is this because the AR10 isn't standardized milspec and therefore the manufactures do not feel the need to go with c-158?

  2. #2
    Join Date
    Sep 2010
    Location
    Northern UT
    Posts
    4,245
    Feedback Score
    69 (100%)
    9310 isn’t necessarily lower grade than C-158, its just available in smaller quantities than c-158 (but cost per pound is more). Also the larger dimension of the ar10 bolt means that there is more material for added strength so c-158 may be unnecessary.
    I paint spaceship parts.

    Quote Originally Posted by Failure2Stop View Post
    Stippled Glocks are like used underwear; previous owner makes all the difference in value.

  3. #3
    Join Date
    Sep 2007
    Location
    AZ
    Posts
    32,833
    Feedback Score
    14 (100%)
    Also... the bolt on an AR-10 is a ham hock compared to the finer AR-15... and subjected to no more PSI.

    I don't know what LMT's AR10 bolt is made from, but that thing takes a filthy beating from Pappabear, and doesn't skip a beat.
    "What would a $2,000 Geissele Super Duty do that a $500 PSA door buster on Black Friday couldn't do?" - Stopsign32v

  4. #4
    Join Date
    Aug 2011
    Location
    N.E. OH
    Posts
    7,595
    Feedback Score
    0
    Quote Originally Posted by markm View Post
    Also... the bolt on an AR-10 is a ham hock compared to the finer AR-15... and subjected to no more PSI.

    I don't know what LMT's AR10 bolt is made from, but that thing takes a filthy beating from Pappabear, and doesn't skip a beat.
    The pressure is the same, but the area exposed to the pressure is greater.
    This means more force on the lugs. Assuming the lugs area is scaled up the same % as as the surface area expised to the pressure is, the pressure on the lugs should be the same as a 5.56 version.

    At least thats me thinking through it mentally, can someone confirm or correct this?

  5. #5
    Join Date
    Dec 2009
    Location
    Utah
    Posts
    8,799
    Feedback Score
    3 (100%)
    Quote Originally Posted by MegademiC View Post
    The pressure is the same, but the area exposed to the pressure is greater.
    This means more force on the lugs. Assuming the lugs area is scaled up the same % as as the surface area expised to the pressure is, the pressure on the lugs should be the same as a 5.56 version.

    At least thats me thinking through it mentally, can someone confirm or correct this?
    Spreading the pressure out over a larger bolt face will reduce stress on the lugs. Using lugs with greater area will further reduce stress.

    Place a nail against a 2x4 and strike it with a hammer. All the force is concentrated into a very small area and the nail is driven into the wood.

    Now, strike the 2x4 using the same hammer using the same force. The blow will leave a dent in the wood, but penetration is shallow. The force of the blow is spread out over a larger area.
    Last edited by MistWolf; 12-11-18 at 16:56.
    The number of folks on my Full Of Shit list grows everyday

    http://i115.photobucket.com/albums/n289/SgtSongDog/AR%20Carbine/DSC_0114.jpg
    I am American

  6. #6
    Join Date
    Mar 2015
    Posts
    1,755
    Feedback Score
    0
    Quote Originally Posted by MegademiC View Post
    The pressure is the same, but the area exposed to the pressure is greater.
    This means more force on the lugs. Assuming the lugs area is scaled up the same % as as the surface area expised to the pressure is, the pressure on the lugs should be the same as a 5.56 version.

    At least thats me thinking through it mentally, can someone confirm or correct this?
    Yes, the pressure is similar, bu the larger area of the .308 case head results in a larger bolt thrust.

    It's about 40% more. However, the bolt is beefier, proportionally speaking....


  7. #7
    Join Date
    Mar 2015
    Posts
    1,755
    Feedback Score
    0
    Quote Originally Posted by MistWolf View Post
    Spreading the pressure out over a larger bolt face will reduce stress on the lugs. Using lugs with greater area will further reduce stress.

    Place a nail against a 2x4 and strike it with a hammer. All the force is concentrated into a very small area and the nail is driven into the wood.

    Now, strike the 2x4 using the same hammer using the same force. The blow will leave a dent in the wood, but penetration is shallow. The force of the blow is spread out over a larger area.
    Not quite true, the load on the bolt face has to be transmitted through the bolt to the lugs, so the surface area of the face has little or no relation to the stress in the lugs. Take for example the Krag bolt with its one lug. The stress in the one lug is higher that that of a Mauser with about twice the locking area, even though the Krag case head is much larger than that of a 8mm Mauser. Primarily, we are interested in the total shear area of the lugs, and a complex calculation to figure out the bending stress of the lugs.

    The area of consideration on the AR design the area is at the base of the lug, seen in orange or red:



    (Incidentally, red indicates that the stress has exceeded the yield limit of the material. This is why AR bolts are subject to low cycle fatigue.)
    Last edited by lysander; 12-11-18 at 17:15.

  8. #8
    Join Date
    Sep 2018
    Posts
    258
    Feedback Score
    0
    Quote Originally Posted by lysander View Post
    Not quite true, the load on the bolt face has to be transmitted through the bolt to the lugs, so the surface area of the face has little or no relation to the stress in the lugs. Take for example the Krag bolt with its one lug. The stress in the one lug is higher that that of a Mauser with about twice the locking area, even though the Krag case head is much larger than that of a 8mm Mauser. Primarily, we are interested in the total shear area of the lugs, and a complex calculation to figure out the bending stress of the lugs.

    The area of consideration on the AR design the area is at the base of the lug, seen in orange or red:



    (Incidentally, red indicates that the stress has exceeded the yield limit of the material. This is why AR bolts are subject to low cycle fatigue.)
    ****ing love it. Proving once again why engineering isn't something you learn from hitting a nail with a hammer and then comparing what happens when you hit a 2x4 with the same hammer.

  9. #9
    Join Date
    Aug 2011
    Location
    N.E. OH
    Posts
    7,595
    Feedback Score
    0
    Quote Originally Posted by MistWolf View Post
    Spreading the pressure out over a larger bolt face will reduce stress on the lugs. Using lugs with greater area will further reduce stress.

    Place a nail against a 2x4 and strike it with a hammer. All the force is concentrated into a very small area and the nail is driven into the wood.

    Now, strike the 2x4 using the same hammer using the same force. The blow will leave a dent in the wood, but penetration is shallow. The force of the blow is spread out over a larger area.
    Same pressure with more area (bolt face) results in higher force. Assuming the lugs are the same size, this means higher force and stress on the lugs.
    As lysander said, the greater lug area brings stress back down.

    Your nail analogy is same force, increased psi. The 308 produces more force, its the same principal that allows a 308 to throw a 147gr projectile the same velocity as a 223 does a 55gr.

    Edit: maybe im using the wrong term. Im saying bolt face meaning where the case and bolt meet. I think you are refering to lug/barrel extension interface.
    Last edited by MegademiC; 12-11-18 at 20:11.

  10. #10
    Join Date
    Dec 2009
    Location
    Utah
    Posts
    8,799
    Feedback Score
    3 (100%)
    Quote Originally Posted by Don Quijote View Post
    ****ing love it. Proving once again why engineering isn't something you learn from hitting a nail with a hammer and then comparing what happens when you hit a 2x4 with the same hammer.
    Quijote, since you're so clever, perhaps you can tell me what the flaw is in my thinking.

    Lysander, Megademic or anyone else, don't help help. I want Mr. "Quickset" to explain it to me. This isn't a trick question, I did make a mistake.
    Last edited by MistWolf; 12-11-18 at 22:56.
    The number of folks on my Full Of Shit list grows everyday

    http://i115.photobucket.com/albums/n289/SgtSongDog/AR%20Carbine/DSC_0114.jpg
    I am American

Page 1 of 2 12 LastLast

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •