Cycling issues in new Grendel build, please help!

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  • gomer
    Unwashed
    • Feb 2017
    • 2

    #31
    I hope to follow your updates, I'm just trying to figure what rifle length buffer setup I'm going to
    run on my current build w/ 22" barrel and rifle length gas, JP SCS. 6.5 G, of course. Debating
    whether I should go standard rifle weight of 5.1 ozs. I guess I can always add. Sorry to get
    off topic a bit - not wanting to hi-jack this thread...

    Comment

    • puncher71
      Bloodstained
      • Jan 2017
      • 25

      #32
      Ok, so got H3 buffer installed and rifle cycled a little better but still not consistent and no hold open on last round. Installed new adjustable gas block. Opened block 1 turn, very little bolt movement, no ejection. 2 turns, cycling but no hold open on last round. 3 turns(almost all the way out on set screw) and we've got hold open. New problem.....for some reason, some casings are not being extracted or ejected but the bolt is locked back. Put bolt back into battery to manually extract and spent casing is pretty tight but not "stuck". This is happening with both reloads and factory Hornady ammo. I never had this issue before when all the other issues were going on!!?? There are no ugly marks on brass that would indicate extractor is ripping violently at the case rim. It may not be gripping with enough pressure? Perhaps I should install an extractor spring upgrade kit? Will a 5.56 extractor work on 6.5 bolt?
      Last edited by puncher71; 03-14-2017, 04:13 AM.

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      • Bwild97
        Warrior
        • Jan 2015
        • 217

        #33
        Yes that would be my next move!

        Comment

        • Rickc
          Warrior
          • Aug 2016
          • 311

          #34
          Originally posted by puncher71 View Post
          Ok, so got H3 buffer installed and rifle cycled a little better but still not consistent and no hold open on last round. Installed new adjustable gas block. Opened block 1 turn, very little bolt movement, no ejection. 2 turns, cycling but no hold open on last round. 3 turns(almost all the way out on set screw) and we've got hold open. New problem.....for some reason, some casings are not being extracted or ejected but the bolt is locked back. Put bolt back into battery to manually extract and spent casing is pretty tight but not "stuck". This is happening with both reloads and factory Hornady ammo. I never had this issue before when all the other issues were going on!!?? There are no ugly marks on brass that would indicate extractor is ripping violently at the case rim. It may not be gripping with enough pressure? Perhaps I should install an extractor spring upgrade kit? Will a 5.56 extractor work on 6.5 bolt?
          oil it up and shoot the hell out of it. It seems that for the first 50 rounds many have cycling problems with grendels. A little overgassed is not a bad thing during this break in period either. then you can adjust your gas block. After they are broke in a little the problem goes away.

          make sure those new mags are loaded full and left loaded for about a week. they need break in too!

          Comment

          • LRRPF52
            Super Moderator
            • Sep 2014
            • 8569

            #35
            Originally posted by puncher71 View Post
            OK, so yall think it is overgassed with the .109 gas port? I beleive the port measurement is correct. With light finger pressure i can twist a 7/64(.109 if my math is correct) drill bit to the bore. My barrel manufacturer has offered to send me an adjustable gas block. If overgassed, that should fix, correct?

            I understand what you say about overgassed bolt moving too fast, but wouldnt it at least eject the spent casing? Sometimes the bolt is still in battery with casing still in chamber after the shot. I assume it blowed back, but cant watch and shoot????
            This is the problem.

            It's getting way too much gas, too fast.

            20" guns are normally some of the smoothest-shooting 6.5 Grendels there are, and the easiest to run reliably from the start.

            All my builds run from the start, but I only get barrels with the correct gas port diameters.

            Been down that road before with 18" MLGS .094" ports, which are way too large for that gas system length.

            Yours should be a .094" (.0935") gas port on a 20" RLGS.

            If the adjustable gas isn't choking it sufficiently, you can try adding carrier weight.
            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

            • ricsmall
              Warrior
              • Sep 2014
              • 987

              #36
              Puncher

              I would try the oring from a 5.56 extractor spring as well as what you've already done. Can't hurt anything.

              Richard
              Member since 2011, data lost in last hack attack

              Comment

              • puncher71
                Bloodstained
                • Jan 2017
                • 25

                #37
                Did some more testing today. The rifle is cycling reliably now and locking back every time on last round, however about one out of every ten rounds fails to extract as mentioned above. I cleaned the chamber to make sure this wasn't the culprit. When I put bolt back into battery on the cases that fail to extract, they manually extract and eject with no effort. I do notice some slight "rolling" of the case rim on these that fail to extract where the extractor is slipping off. I believe the spring is too weak or the extractor claw is not getting enough purchase on the case rim. I've got BCM spring upgrade kit with O ring on the way. Hope this solves it. On a positive note, this thing is driving tacks! One ragged hole after ragged hole.

                Comment

                • LRRPF52
                  Super Moderator
                  • Sep 2014
                  • 8569

                  #38
                  Your timing is off. The extractor spring is fine for a normal .094" gas port RLGS, but you need to add carrier and buffer weight I think.

                  Or just get another barrel with the correct port diameter.

                  Lighter bullets will work better, but you shouldn't have to limit your projectile selection because someone cut the wrong port.
                  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

                  • puncher71
                    Bloodstained
                    • Jan 2017
                    • 25

                    #39
                    It doesn't seem that timing or the gas system is my problem now that I have the adjustable gas block tuned and an H3 buffer installed. As mentioned earlier, the rifle is cycling correctly, ejecting a nice pile at 4 o'clock and hold open on every last round. There is now just the occasional failure to extract. I have compared the extractor spring tension on this 6.5 bolt to several other bolts I have in 5.56 and 7.62x39 and the 6.5 feels slightly weaker. Anyway, upgrade kit on its way, so we shall see. Thanks for yalls input.

                    Comment

                    • puncher71
                      Bloodstained
                      • Jan 2017
                      • 25

                      #40
                      Installed BCM enhanced extractor spring kit and same issues, BUT a new development!! I noticed cases are fitting very sloppy in bolt face, so I measured and interior dimension of bolt face is .475. As I'm sure you experts know, Grendel case rim specs are .4449. Obviously with so much play in this bolt face, it is easy for the extractor to not get a good grip if that case is shifted over .025. I have messaged my barrel manufacturer about getting correct bolt. I have also read where folks are using 7.62x39 bolts interchangeably with the Type 1 Grendel bolts. I have a 7.62x39 bolt and the case fit is much better. I just wanted to check with yall about using the 7.62x39 bolt in my Grendel. The bolt head spaces correctly with my barrel, but I didn't want to test fire it until I a gathered more info.

                      Comment

                      • ricsmall
                        Warrior
                        • Sep 2014
                        • 987

                        #41
                        You should be fine as long as headspace is hood. Extractor lip is a little thinner on that bolt, so stout loads may break it. Should b ok temporarily

                        Richard
                        Member since 2011, data lost in last hack attack

                        Comment

                        • LRRPF52
                          Super Moderator
                          • Sep 2014
                          • 8569

                          #42
                          Originally posted by puncher71 View Post
                          It doesn't seem that timing or the gas system is my problem now that I have the adjustable gas block tuned and an H3 buffer installed. As mentioned earlier, the rifle is cycling correctly, ejecting a nice pile at 4 o'clock and hold open on every last round. There is now just the occasional failure to extract. I have compared the extractor spring tension on this 6.5 bolt to several other bolts I have in 5.56 and 7.62x39 and the 6.5 feels slightly weaker. Anyway, upgrade kit on its way, so we shall see. Thanks for yalls input.
                          Failure to extract is one of the telltale signs of too fast of a cyclic rate.

                          When the case is obdurated to the chamber walls, but the action is already on its way rearward, you often get extractor slip, resulting in FTExtract.

                          Increased extractor spring or O ring addition is a band-aid for it that works, but the fundamental problem of over-gassing is still present.

                          It can also be caused by a rough chamber with tool marks all over or in certain places that haven't been polished out.
                          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

                          • puncher71
                            Bloodstained
                            • Jan 2017
                            • 25

                            #43
                            Spoke to barrel maker and he said if bolt face was .475 then I was mistakenly shipped a .458 socom bolt. He is going to make it right.

                            Comment

                            • LRRPF52
                              Super Moderator
                              • Sep 2014
                              • 8569

                              #44
                              Measure the face depth of that SOCOM bolt while you're at it.

                              I blew past your last post on the previous page. That explains the FTEtract big time.
                              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

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