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what does S.D. mean in this context?

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  • Big Chudungus
    Veteran Member
    • Jun 2021
    • 3123

    what does S.D. mean in this context?

    (they are talking about Tika Arctic bolt action 308)

    We clocked and grouped three types of rounds. First up, Remington Premier Match 168-grain Matchking BTHP ran at 2,487 fps, with an eye-twitching S.D. of 37.2. Next up, Hornady’s Precision Hunter 178-grain ELD X ran at 2,488 fps, with a very respectable S.D. of 12.3.
  • #2
    Fjold
    I need a LIFE!!
    • Oct 2005
    • 22896

    Standard deviation - How much variance in velocity of each shot. The lower the value of the SD, the more consistent your velocities are and usually the more accurate they they will be. With one of my match loads a difference in velocity of 100 fps at the muzzle will result in a difference of a 8" in elevation at 1,000 yards.

    It's basically the average difference from the average velocity of a string of shots. You can find the complete formula on line. Many chronographs have the ability to calculate the SD and give you the result from each shot string.
    Frank

    One rifle, one planet, Holland's 375




    Life Member NRA, CRPA and SAF

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    • #3
      Big Chudungus
      Veteran Member
      • Jun 2021
      • 3123

      thx, when he said "eye-watering" I thought maybe it was muzzle-blast/fire-ball face concussion. lol.

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      • #4
        smoothy8500
        Veteran Member
        • Sep 2009
        • 3846

        Originally posted by Big Chudungus
        (they are talking about Tika Arctic bolt action 308)

        eye-twitching S.D. of 37.2..........with a very respectable S.D. of 12.3.
        In the grand scheme of things, the difference between 12 and 37 is really not that big a deal.

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        • #5
          Experimentalist
          Banned in Amsterdam
          CGN Contributor - Lifetime
          • May 2006
          • 1171

          Originally posted by smoothy8500
          In the grand scheme of things, the difference between 12 and 37 is really not that big a deal.
          Depends on application. For hunting, plinking, etc. you're correct.

          For precision rifle use hand-loaders strive for single digit Standard Deviations.

          "An unarmed man can only flee from evil. And evil is not overcome by fleeing from it" - Col. Jeff Cooper

          "Shot placement trumps all."

          Originally posted by CSACANNONEER
          Who uses 9mm for SD? Anything less than a 50BMG is stupid to use. Personally, I prefer canister rounds out of a 10lb Parrott rifle for SD.

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          • #6
            Fjold
            I need a LIFE!!
            • Oct 2005
            • 22896

            Originally posted by smoothy8500
            In the grand scheme of things, the difference between 12 and 37 is really not that big a deal.
            Standard Deviation is the square root of the difference.

            If you had a ten-shot group with a mean (middle value) of 2754 fps and an extreme spread of 16 fps, you would have a Standard Deviation of 5.5 fps (very good)

            The same size sample group at the same mean (2,754 fps) with an extreme spread of 37 fps, would get you a SD of 9.5 fps (still good)

            The same size sample at a mean of 2,754 with an extreme spread of 53 fps gives you a standard deviation of 13.1 fps (still OK)

            If you have a Standard Deviation of 37 fps, then you are talking about extreme spreads of more than a couple of hundred fps. (terrible). You would see noticeable vertical stringing at distance.
            Last edited by Fjold; 03-02-2025, 1:49 PM.
            Frank

            One rifle, one planet, Holland's 375




            Life Member NRA, CRPA and SAF

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            • #7
              smoothy8500
              Veteran Member
              • Sep 2009
              • 3846

              Originally posted by Fjold
              With one of my match loads a difference in velocity of 100 fps at the muzzle will result in a difference of a 8" in elevation at 1,000 yards.....
              You would see noticeable vertical stringing at distance.
              Yes, we strive for lower velocity spread. It is true that there will be influence on vertical stringing. But, 95% of the rounds will be within 4 SD's; 148fps

              As evident by your example, a little over one (1) MOA at 1,000 yds.....

              Well within most shooter's margin of error at 1K, and not really that big of a deal at 600.

              Comment

              • #8
                Scotty
                Senior Member
                • Dec 2005
                • 1736

                68% of the rounds will be +/- one SD from the average. 95% will be +/- two SD from the average.

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                • #9
                  W.R.Buchanan
                  Veteran Member
                  • Jan 2008
                  • 3374

                  OK: Changes in Velocity equal Changes in Trajectory. Changes in Trajectory equal changes in Elevation at the Point of Impact. Obviously that means changes in group size at your given Range.

                  I have a friend who is a high end Bench Rest shooter. he recently shot a 5 shot group at 1000 yards that measured .968" his SD for that load was 1.4 !!!

                  At my level of shooting an SD of <40 would be fantastic and no gun that I own would shoot better than that, and I could not shoot better than that, and neither could 95% of the shooters out there.

                  Something to consider ? But not necessarily overlook?

                  Randy
                  Rule #1 Liberals screw up everything they touch.
                  Rule #2 Whatever they accuse you of, they are already doing.
                  Rule #3 Liberals lie about anything no matter how insignificant.
                  Rule #4 If all else fails, they call you a Racist!

                  It's not how well you do what you know how to do,,, It is how well you do what you don't know how to do.
                  www.buchananprecisionmachine.com

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                  • #10
                    Fjold
                    I need a LIFE!!
                    • Oct 2005
                    • 22896

                    If you have 2 MOA eyes, a 2 MOA gun and 2 MOA of standard deviation, you have a gun that will shoot 6" groups at 100 yards.
                    Frank

                    One rifle, one planet, Holland's 375




                    Life Member NRA, CRPA and SAF

                    Comment

                    • #11
                      Markbsae
                      Junior Member
                      • Jul 2023
                      • 90

                      Originally posted by W.R.Buchanan
                      I have a friend who is a high end Bench Rest shooter. he recently shot a 5 shot group at 1000 yards that measured .968" his SD for that load was 1.4 !!!

                      Randy
                      that's insane!

                      Comment

                      • #12
                        W.R.Buchanan
                        Veteran Member
                        • Jan 2008
                        • 3374

                        Originally posted by Markbsae

                        that's insane!
                        I saw the Target! I was blown away.

                        Randy
                        Rule #1 Liberals screw up everything they touch.
                        Rule #2 Whatever they accuse you of, they are already doing.
                        Rule #3 Liberals lie about anything no matter how insignificant.
                        Rule #4 If all else fails, they call you a Racist!

                        It's not how well you do what you know how to do,,, It is how well you do what you don't know how to do.
                        www.buchananprecisionmachine.com

                        Comment

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