Again. Twist rate for 6,5 Grendel

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  • Second
    Warrior
    • Oct 2017
    • 240

    Again. Twist rate for 6,5 Grendel

    First post.
    Always a first

    Are starting up a custom build of a bolt action 6,5 Grendel with a friend.
    Have ended up with what barrel to use, and the twist rate.

    Bullets that I intend to use is 120-130gr.
    Mostly the Lapua Scenar L in 120gr, Scenar 123gr.
    The Hornady ELD 123gr and ELD 130gr.
    Might be lighter Lapua bullets also, but this is not something that will be in the desicion.

    Barrel length will be about 18-20", and a supressor will most likely.

    Have made some diffrent calculations on the Berger Bullets Twist rate stability calculator with this bullets.
    It seems that 1:7,5 gives good figures, better than the same in 1:8 twist.
    But when I search the internet, the 1:8 and also 1:9 is more common.

    Any thoughts on this forum?
  • kmon
    Chieftain
    • Feb 2015
    • 2095

    #2
    I have no problems with the 130 Berger and Nosler 129 LRAB in a 1:8.4 22 inch Obermeyer on the CZ 527. From your 18 or 20 inch I would think 1:8 will be just fine.

    I also shoot a 6.5-284 with 24 inch 1:9 twist that works very well with the 140gr Bergers.

    Comment

    • VASCAR2
      Chieftain
      • Mar 2011
      • 6219

      #3
      Brian Litz from Applied Ballistics has done much research in regards to barrel twist and I suggest you check out his web site. The trend is for longer higher BC bullets whether cup and core lead or monolithic bullets. I don’t think the 6.5 Grendel has enough case capacity to drive the bullets fast enough to be over stabalized with a 1:7.5 twist. With a very long high BC bullet a 1:7.5 twist could stay more stable through the transonic zone at distances beyond 1000 meters.

      If your never going to shoot past 600-700 meters I don’t think you will see a significant difference between 1:7.5 twist compared to 1:8 twist. If you regularly shoot at long range beyond 800-900 meters with 130 grain bullets you might consider the 1:7.5 twist. I’ve been reading about long range shooting for many years and bought my first 6.5 Grendel in 2009. There has been significant advances in research and available bullets in that period of time. When I bought my first 6.5 Grendel 1:9 twist was the most common twist rate. The research conducted by Bill Alexander showed shorter 6.5 Grendel barrels were more accurate with faster twist 1:7.5.

      There are bullets now that were not available when Bill Alexander was developing the 6.5 Grendel. I’m not a good enough shooter at long range to probably ever see a significant difference between 1:7.5 and 1:8 twist. I’m not sure there is a right ot wrong answer as long as you buy a quality barrel.

      Last edited by VASCAR2; 10-18-2017, 03:56 PM.

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      • Second
        Warrior
        • Oct 2017
        • 240

        #4

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        • Second
          Warrior
          • Oct 2017
          • 240

          #5

          Comment

          • LRRPF52
            Super Moderator
            • Sep 2014
            • 8569

            #6
            If you can get 1/7.5" twist, get it.

            Bill Alexander did a lot of testing with this, and found that for 18" and shorter, 1/7.5" provided the best stability.

            Since you're using a bolt action, you will be able to get better numbers than those.

            I know the guys at Lapua who did the testing. They pushed 8gram Scenars to some pretty insane speeds, but the brass was trashed.

            Keeping it reasonable, you can push the 123gr Scenar to 2600fps even from an 18" barrel with the right powder.

            The Vihtavuori data seems to be very conservative with maybe a buffer underneath SAAMI pressure.

            If you're using a SAKO action, it will handle more pressure than the AR15 barrel tennon's relief cut on the threads, which is the weak link.
            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

            • BluntForceTrauma
              Administrator
              • Feb 2011
              • 3897

              #7
              There is no downside to going with 1:7,5 versus a 1:8. When in doubt, go with a tighter twist. Will help in worst-case scenarios: sea level, -18 degrees C, long bullets.
              :: 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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              • AZHTfreak
                Warrior
                • Jan 2017
                • 316

                #8
                What are the effects of over stabilizing?
                DOJ+FBI+IRS+AFT=NKVD. Joe Stalin and Lavrentiy Pavlovich Beria are tap dancing in hell right now...

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                • Second
                  Warrior
                  • Oct 2017
                  • 240

                  #9
                  The buld will be made on a Remington 700 SA in .222Rem.
                  Blueprinted and opened boltface to fit the 6,5 Grendel from Laupa.

                  Will check for an 1:7,5 twist, but if a 1:8 twist falls in my lap for a good price, then it will probably work too.

                  For the calculations on the twist I have used +10 degrees C on all diffrent bullets, speeds, twists, etc. But this rifle will probably be used also in really low degrees. -20 degrees C is not uncommon when hunting in January in the north of Sweden for the capercaillie.

                  Comment

                  • Klem
                    Chieftain
                    • Aug 2013
                    • 3507

                    #10
                    Originally posted by AZHTfreak View Post
                    What are the effects of over stabilizing?
                    The bullet will resist pointing along the ballistic curve after apogee. It points along the barrel axis until apogee but then resists pointing down towards the target. it still wants to point towards the sky. This means there's a degree of yaw in the last 1/3 of its flight.

                    Comment

                    • LRRPF52
                      Super Moderator
                      • Sep 2014
                      • 8569

                      #11
                      Originally posted by Klem View Post
                      The bullet will resist pointing along the ballistic curve after apogee. It points along the barrel axis until apogee but then resists pointing down towards the target. it still wants to point towards the sky. This means there's a degree of yaw in the last 1/3 of its flight.
                      I've actually seen the effects of that at ELR.

                      Shooting aluminum Jaster targets in Europe, you could see repeatable, multiple hits of bullets that didn't nose over after apogee/maximum ordinate. Pretty cool to see that they were still impacting with repeatability.

                      This was with 7mm and .338 Lapua Magnum Long Range rifles out at over 1300m. Terminal effects would be pretty devastating.
                      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

                      • mdram
                        Warrior
                        • Sep 2016
                        • 941

                        #12
                        i have found 1 1:7.5 twist that i can recall
                        that was tbox barrels
                        just some targets for printing
                        https://drive.google.com/drive/folde...xQ?usp=sharing

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                        • Second
                          Warrior
                          • Oct 2017
                          • 240

                          #13

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                          • stilesg57
                            Unwashed
                            • Sep 2017
                            • 24

                            #14
                            I would've taken 7.5 if I could get it in the rifle I wanted, but given that

                            1) I never expect to handload and therefore will rarely shoot anything over 123 grains;

                            2) I'm only doing 24" barrels; and

                            3) I'll likely only shoot it between 4,000-9,000ft above sea level, I don't fret a 1:8 twist. Your situation might be different though: heavier bullets, shorter barrels, and lower altitudes will let faster twists shine a bit more. If you're having a custom barrel made, I think 1:7.5 is generally a better call than 1:8.

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