What bolt lugs? Who needs those?

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  • Difranco
    Unwashed
    • Nov 2014
    • 19

    What bolt lugs? Who needs those?

    Almost three years ago I bought a barrel and bolt from AR Build a box gentleman on this site.

    I put a little 6.5 Grendel Starter Kit together that is a great way to get into this cartridge. The kit includes: New Brownell's 18" MLGS Stainless Barrel/bolt combo * Blended and polished feed ramps to help with feeding and reducing brass wear * Headspaced Correct Grendel bolt * Radiused ejector for optimal


    Anyway built the rifle and everything seemed fine, mounted a scope sighted it in and got the gas key tuned right. Probably only put at most 40 rounds of Hornady factory ammo through it. Took it out for deer season in 2015. Hadn't touched the rifle since. I only had a low end Nikon scope on it. So I just bought a new scope and went out to sight in the scope today.

    8 rounds into the day... A failure to feed. My bolt no longer had any lugs on it. And after a full tear down of the upper, it appears the lug at the 6 o'clock position on the barrel extension is broke off at the top / tip as well.

    I've only shot factory Hornady ammo, none of the cases from today were deformed or showed any sign of over pressure. Chamber and bore look fine. So I'm chalking this up to a defective bolt.

    Does a Grendel barrel use a standard M4 extension that is used for a 5.56 barrel?
    When you clean the vacuum cleaner you become the vacuum cleaner.
  • Difranco
    Unwashed
    • Nov 2014
    • 19

    #2
    1505712648193_1.jpg

    any help is appreciated.
    When you clean the vacuum cleaner you become the vacuum cleaner.

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    • NugginFutz
      Chieftain
      • Aug 2013
      • 2622

      #3
      Not much left there for a post-mortum!

      To answer your question, the barrel extension is that same as for any other M4 or Rifle style barrel, 5.56 included. Ramp profile should match the upper receiver's, but no real considerations, beyond that. Some will polish the ramps, but that should not have anything to do with bolt failures.

      I suppose the first question is which bolt manufacturer and which barrel? I've not seen damage like that in some while. While you assembled that one, yourself, I would definitely let LRRPF52 know about this one.

      Next, I would ask "did you lap your upper receiver face?" Poor bolt and extension alignment has been known to cause issues like this. If the barrel is mounted off-axis due to an imperfect receiver face, bolt lugs can (and have) be known to let go.

      If you have not lapped the upper, or if the barrel to upper fit is loose (consider bedding the barrel), then just throwing another bolt in could end up in the same way.

      Either way, I suspect '52 will be along and offer further (enhanced) advice and information.

      Good Luck, Difranco.
      If it's true that we are here to help others, then what exactly are the others here for?

      Comment

      • Difranco
        Unwashed
        • Nov 2014
        • 19

        #4
        It's a Brownells barrel and bolt as described in the sales post. I didn't lap the receiver face, but it is a quality Aero Precision upper. The barrel fit nice and snug into the receiver and didn't require any bedding. Bushing torqued to spec. There weren't any unusual wear marks on the lugs or bolt face.

        The rifle was shooting sub MOA btw.
        Last edited by Difranco; 09-18-2017, 02:21 PM.
        When you clean the vacuum cleaner you become the vacuum cleaner.

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        • bj139
          Chieftain
          • Mar 2017
          • 1968

          #5
          Doesn't Brownells have a lifetime guarantee against manufacturing defects for anything they sell?

          Comment

          • NugginFutz
            Chieftain
            • Aug 2013
            • 2622

            #6
            Originally posted by Difranco View Post
            It's a Brownells barrel and bolt as described in the sales post. I didn't lap the receiver face, but it is a quality Aero Precision upper. The barrel fit nice and snug into the receiver and didn't require any bedding. Bushing torqued to spec. There weren't any unusual wear marks on the lugs or bolt face.

            The rifle was shooting sub MOA btw.
            I like Aero Precision stuff, as well but, whenever possible, I always at least check the face for squareness. In my experience, forged uppers tend to be out most often.

            I'm no machinist or metallurgist, but the crystalline appearance past the hardened surfaces is not what I would have expected. Strange.

            bj also brings up an excellent point. It's certainly worth a call to see if they will replace the bolt.
            If it's true that we are here to help others, then what exactly are the others here for?

            Comment

            • Difranco
              Unwashed
              • Nov 2014
              • 19

              #7
              I don't if they do or not and if it extends to the end user or if I need to return it to the "retail" seller in order to get them to honor it. I got on Brownells chat the lady stated that they have a "forever" warranty on their parts.

              The bolt extension needs to be replaced as well, the lug at 6 o' clock is chipped off.
              Last edited by Difranco; 09-18-2017, 04:56 PM.
              When you clean the vacuum cleaner you become the vacuum cleaner.

              Comment

              • Difranco
                Unwashed
                • Nov 2014
                • 19

                #8
                Originally posted by NugginFutz View Post
                I like Aero Precision stuff, as well but, whenever possible, I always at least check the face for squareness. In my experience, forged uppers tend to be out most often.

                I'm no machinist or metallurgist, but the crystalline appearance past the hardened surfaces is not what I would have expected. Strange.

                bj also brings up an excellent point. It's certainly worth a call to see if they will replace the bolt.
                That crystalline appearance surprised me as well. What is useful to notice, that bolt lugs are all remained perfectly shaped, no dings - dents.... it like they were just peeled off the bolt.
                Last edited by Difranco; 09-18-2017, 05:07 PM.
                When you clean the vacuum cleaner you become the vacuum cleaner.

                Comment

                • LRRPF52
                  Super Moderator
                  • Sep 2014
                  • 8569

                  #9
                  Got any pics of the barrel extension?

                  If the barrel extension and bolt are both damaged, that's important to look at.

                  I'm also wondering what the brass looks like from the fired round.

                  Looks like the extractor is still intact, is that right?
                  Last edited by LRRPF52; 09-18-2017, 05:20 PM.
                  NRA Basic, Pistol, Rifle, Shotgun, RSO

                  CCW, CQM, DM, Long Range Rifle Instructor

                  6.5 Grendel Reloading Handbooks & chamber brushes can be found here:

                  www.AR15buildbox.com

                  Comment

                  • Difranco
                    Unwashed
                    • Nov 2014
                    • 19

                    #10
                    Here are pics of the barrel, extension. The 6 O'clock lug has been topped off, I suspect this occurred when the bolt rotated and the bolt lugs falling off. That shot / recoil felt totally normal, case ejected normally, the only reason I new something was up was because it failed to feed. Brass was from Hornady factory ammo, no flattened primers or anything indicating an over pressure (no cratered primer, etc.)
                    Attached Files
                    When you clean the vacuum cleaner you become the vacuum cleaner.

                    Comment

                    • LRRPF52
                      Super Moderator
                      • Sep 2014
                      • 8569

                      #11
                      I'm leaning towards poor metallurgy on the bolt as well.

                      Something is definitely wrong with bolt metallurgy to see that many bolt lugs shorn off, with the extractor still intact and functioning even.
                      NRA Basic, Pistol, Rifle, Shotgun, RSO

                      CCW, CQM, DM, Long Range Rifle Instructor

                      6.5 Grendel Reloading Handbooks & chamber brushes can be found here:

                      www.AR15buildbox.com

                      Comment

                      • Lastrites
                        Warrior
                        • Apr 2017
                        • 678

                        #12
                        The question is whether or not Brownells will warranty a bolt that had passed hands from the original seller. I would like to think yes they would but deserves a call to confirm.

                        Comment

                        • mdram
                          Warrior
                          • Sep 2016
                          • 941

                          #13
                          garunteed forever

                          just some targets for printing
                          https://drive.google.com/drive/folde...xQ?usp=sharing

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                          • BluntForceTrauma
                            Administrator
                            • Feb 2011
                            • 3897

                            #14
                            Didn't know they made bolts from cast iron?
                            :: 6.5 GRENDEL Deer and Targets :: 6mmARC Targets and Varmints and Deer :: 22 ARC Varmints and Targets

                            :: I Drank the Water :: Revelation 21:6 ::

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                            • Difranco
                              Unwashed
                              • Nov 2014
                              • 19

                              #15
                              Originally posted by mdram View Post
                              Only to the original purchaser. No order number, no return. Just got off the phone with them.
                              When you clean the vacuum cleaner you become the vacuum cleaner.

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