Does 65G + EPR = GPC ?

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  • stanc
    Banned
    • Apr 2011
    • 3430

    Does 65G + EPR = GPC ?



    The premise that 6.5 Grendel is capable of replacing 7.62 NATO as well as 5.56 NATO was originally based on ballistics data of the 123gr 6.5 Scenar match hollow point versus the 147gr 7.62 M80 full metal jacket loads.

    Since that time, the US Army adopted the lead-free M80A1 to supersede the lead-core M80, thereby rendering conclusions based on the Scenar/M80 comparisons of little or no value in determining if 6.5 Grendel is a viable option for a General Purpose Cartridge.

    If 6.5 Grendel ballistic superiority depends upon having a projectile weight of 123 grains, this creates some issues in switching from lead-core to lead-free projectiles, due to the increase in bullet length necessary with the lower-density materials used (steel and copper).

    The lead-core, 123gr Scenar is itself rather long (1.3"), and eats up a significant amount of powder space in the cartridge case as a result (below, right).



    Muzzle velocity of a 123gr bullet from a 16" barrel is very modest, only 2350 fps for the Hornady 123gr SST load. http://www.hornady.com/store/6.5-Grendel-123-gr-SST/

    A 123gr lead-free projectile of the M80A1 type (below) would be at least 1.4" long, if not longer, further reducing powder capacity. Which would presumably have a negative impact on muzzle velocity, trajectory, wind drift, and terminal effects.



    The alternative is to opt for a shorter bullet, that would have minimum extension into the propellant space. Shorter equals lighter, which -- together with potentially greater powder charge -- means muzzle velocity would be much higher. Unfortunately, shorter and lighter also means lower BC, which adversely affects ballistic performance.

    So, the question is, what would be the best weight for such a 6.5mm lead-free projectile, so as to achieve the optimum balance of ballistics and terminal effects, and would its performance be good enough to be a viable replacement for 7.62 M80A1?

    Last edited by stanc; 04-30-2017, 11:39 PM.
  • A5BLASTER
    Chieftain
    • Mar 2015
    • 6192

    #2
    I would put my thinking in a bullet say 100 grain made with the specs of one of the new cavity back bullets, think it would be short enough and hold enough weight and with the cavity in the back of the boat tail it would allow more powder in the case increasing MV in the shorter barrels the military use's.

    I could be way off but that is my idea, what you think stanc.

    Comment

    • stanc
      Banned
      • Apr 2011
      • 3430

      #3
      It sounds like an interesting concept, but such projectiles are kinda off topic for this thread.

      I'm looking for input on optimum weight and length of an EPR bullet for 6.5 Grendel, using the same type of construction as in the M80A1: exposed steel penetrator, copper slug, reverse drawn jacket.

      Comment

      • VASCAR2
        Chieftain
        • Mar 2011
        • 6219

        #4
        It would be interesting to see what kind of BC could be achieved with 6.5/.264 100, 107, 110 and 113 grain EPR. A compact bullpup with 16-18 inch barrel in 6.5 Grendel with 107 grain EPR at 2650 FPS might prove very effective. A 14 1/2" M-4 with a 100 grain EPR 6.5 MM at 2550 FPS would be intersting to test. Anyone have any idea what velocity threshold the EPR would require to fragment?

        Comment

        • LRRPF52
          Super Moderator
          • Sep 2014
          • 8569

          #5
          The Hornady data is for a 14.5" AA Grendel with 123gr that was pinned to 16" with the muzzle device to keep it out of NFA territory, not a 16" barrel.

          2350fps is pretty slow for a 14.5" barrel with a 123gr as well, maybe typical of colder temps.

          I don't know what the weight is of the existing 6.5 Grendel EPR projectile, but the BC is similar to a 123gr Scenar. The weight is less than 123gr though from what I was told.

          It defeats the NATO CRISAT from a 14.5" barrel at 450m.
          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

          • stanc
            Banned
            • Apr 2011
            • 3430

            #6
            Originally posted by LRRPF52 View Post
            I don't know what the weight is of the existing 6.5 Grendel EPR projectile, but the BC is similar to a 123gr Scenar. The weight is less than 123gr though from what I was told.
            A 6.5 Grendel EPR bullet has been developed? Verrrry interesting. Is it possible to get photos, weight, BC?

            Comment

            • stanc
              Banned
              • Apr 2011
              • 3430

              #7
              Originally posted by VASCAR2 View Post
              It would be interesting to see what kind of BC could be achieved with 6.5/.264 100, 107, 110 and 113 grain EPR.
              Indeed it would. Since no info is available on the EPR projectile that is said to have been developed specifically for 6.5 Grendel, I came across the next best thing.

              From TFB, a design for an "optimized" 6.5mm 108gr EPR. http://www.thefirearmblog.com/blog/2...nition-part-2/

              BC = 0.246 G7

              Comment

              • BluntForceTrauma
                Administrator
                • Feb 2011
                • 3897

                #8
                Stan, cool find.

                Author notes a velocity of 2,550 fps. He happen to mention barrel length?

                From a 20" bbl with the 6.5 108 Lapua Scenar Grendel shooters get 2790 fps with 29.7 XBR at 2.260 COL.
                :: 6.5 GRENDEL Deer and Targets :: 6mmARC Targets and Varmints and Deer :: 22 ARC Varmints and Targets

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

                Comment

                • stanc
                  Banned
                  • Apr 2011
                  • 3430

                  #9
                  John, I saw no mention of barrel length in the article. My take is that he wasn't concerned about what barrel length would be required to actually achieve that velocity.

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