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  • SD and Extreme Spread

    For you technical oriented shooters that stayed awake in Math class.
    http://www.mssblog.com/2019/08/09/re...d-deviation-2/

  • #2
    Bud had a .35 whelen that shot crappy. Powder was not great for case capacity. Checked w Chrono.
    Std dev was bad. Used a filler w same load.....std dev went small. Groups good. Whod have thunk it. Lol.

    I dont have a chronograph. My junk shoots good. I run compressed loads. Good enough.

    As for math.....machine design was ok. Thermo sucked
    Calc i hated but physics statics and dynamics was fun

    Comment


    • #3
      My ex went to a state school on tennis scholarship.

      Nice legs.

      Two of them.

      ' cause I aint into doin' pirates

      Comment


      • #4
        I was shooting at 600 to 1100 yards all afternoon yesterday. Standard Deviation was the most important variable. I watched SD's religiously as I tested a new 25 Creedmoor I just finished ( I necked down a 6.5 CM and was testing the 131g ACE .257 bullet) and a variety of loads. If the bullets aren't all traveling at almost the exact same velocity, they get vertically distributed at the target as gravity drops one shot more than the others.

        The question is "How do I get low SD's"?

        First, I prepare my cases as uniformly as I can so that I get the most consistent explosion of propellant possible. I fire-form cases so I don't experience variations in pressure as cases expand to chamber dimensions; I trim case length, chamfer the necks, chamfer the inside of the flash hole, turn the necks to exactly the same thickness (usually .015").

        Next, I weight and sort the cases, bullets and powder charges all to .1g of variance. When done, each "ready to fire" cartridge used within a test group weighs exactly the same as its group counterparts to within .1g.

        Finally, I coat each bullet with Hexagonal Boron Nitride (h-BN), another important contributor to low SD's. It is about our best bullet lubricant. It seems to significantly contribute to low SD's by producing low and consistent friction as the bullet travels through the bore. Since it reduces peak pressure during the charge's propulsion, it occasionally allows me to inch up to a higher velocity accuracy node that produces real low SD's that I couldn't otherwise reach. Finally, it contributes to keeping the bore clean and consistent from shot to shot.

        I test powders and loads to find a combination that burns most consistently according to velocity. I don't stop testing until I find a load that produces an SD of 10 or lower across five consecutive shots (I try to obtain a load with less than a 5 SD). I then test various seating depths to find the lowest SD and most accurate load possible. For shooting 1000 yards and beyond, an SD of 10 or less is mandatory for predictable bullet impact as bullet drop begins to vary by a foot or more as SD's exceed 10.

        Of course none of this makes any difference if you are trying to harvest a deer at 25 yards under a corn feeder but I enjoy experimenting and being as predictable at 1000 yards as most shooters are at 100 yards. The pursuit of long range precision has provided me a year-round hobby as I try to hone my shooting skills beyond what I have done in the past. I'm making custom rifles and custom cartridges to push the envelope and it has been fun learning and experimenting.
        Last edited by DakotaMan; 08-11-2019, 10:05 AM.

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        • #5
          IIRC w the filler to gobble air space, the finally accurate load for my bud's .35 had a SD of 9.
          Long time ago, might have been 12 or 15. But I think single digits. Some other stuff we ran might have been the doubles I mention.

          Cases.... same lot, flash holes uniformed, neck sized and no air gap in powder charge.
          Gets me sub .5" at 100.
          That my " good enough for chucks" loading.
          My old BDL was around .25".......but looked like hell (prev owner carried in truck rack- hardly shot though). I refinished the stock, bedded the action...........and stepson saw the rifle flash all the way across the pasture (yote hunting).
          So when somebody offered me more than I had in it........away it went.
          Replacement rifle (synth , matte)..........did .5" so was OK.
          Still not the zinger the prev .243 was.

          Reloading room still not done, so running factory in my current clunker ADL. Getting .75" @ 100. Have no idea what propellant or % capacity the WW 80gr stuff is.

          The back room is kinda outdoorsy. Ol lady said I could put a retro industrial bench by back window. Suppose I could mount a Lyman T mag on it?
          Hope she's cool w orange.

          Comment


          • #6
            Originally posted by DakotaMan View Post
            I was shooting at 600 to 1100 yards all afternoon yesterday. Standard Deviation was the most important variable. I watched SD's religiously as I tested a new 25 Creedmoor I just finished ( I necked down a 6.5 CM and was testing the 131g ACE .257 bullet) and a variety of loads. If the bullets aren't all traveling at almost the exact same velocity, they get vertically distributed at the target as gravity drops one shot more than the others.

            The question is "How do I get low SD's"?

            First, I prepare my cases as uniformly as I can so that I get the most consistent explosion of propellant possible. I fire-form cases so I don't experience variations in pressure as cases expand to chamber dimensions; I trim case length, chamfer the necks, chamfer the inside of the flash hole, turn the necks to exactly the same thickness (usually .015").

            Next, I weight and sort the cases, bullets and powder charges all to .1g of variance. When done, each "ready to fire" cartridge used within a test group weighs exactly the same as its group counterparts to within .1g.

            Finally, I coat each bullet with Hexagonal Boron Nitride (h-BN), another important contributor to low SD's. It is about our best bullet lubricant. It seems to significantly contribute to low SD's by producing low and consistent friction as the bullet travels through the bore. Since it reduces peak pressure during the charge's propulsion, it occasionally allows me to inch up to a higher velocity accuracy node that produces real low SD's that I couldn't otherwise reach. Finally, it contributes to keeping the bore clean and consistent from shot to shot.

            I test powders and loads to find a combination that burns most consistently according to velocity. I don't stop testing until I find a load that produces an SD of 10 or lower across five consecutive shots (I try to obtain a load with less than a 5 SD). I then test various seating depths to find the lowest SD and most accurate load possible. For shooting 1000 yards and beyond, an SD of 10 or less is mandatory for predictable bullet impact as bullet drop begins to vary by a foot or more as SD's exceed 10.

            Of course none of this makes any difference if you are trying to harvest a deer at 25 yards under a corn feeder but I enjoy experimenting and being as predictable at 1000 yards as most shooters are at 100 yards. The pursuit of long range precision has provided me a year-round hobby as I try to hone my shooting skills beyond what I have done in the past. I'm making custom rifles and custom cartridges to push the envelope and it has been fun learning and experimenting.
            At a range I sometimes shoot at they host bench rest competition. The guys have their cases marked and insert them into the chamber in exactly the same orientation every time.
            I often wonder how homogenous powder is within a pound. I wish I still had access to a lab bomb. We could take a small sample and ignite it and measure the gas produced. My feeling is the powder has some small variation across the pound container.

            When I was doing load work up I would roll the bullet on a shop rag moist with Mobil 1. Also tried the graphite and coated some of my bullets. My measuring techniques were not sensitive enough to detect small changes.

            Remington has just recently introduced a new handgun load - the 'Black Belt'. The bullet has a hourglass waist and there is a polymer black band that fills the crease. Suppose to lubricate and center to the bore better. They shoot fine in my handgun.

            Remington has a new 700 called the American Hunter. Blue printed action and a R-5 rifling that has a land opposite a grove which is suppose to yield better harmonics. Other features that I can't remember. Jim Just got a new magazine to read.

            Comment


            • #7
              I'm a slob. Content to pop golf balls off posts at 200.
              Hell, was doing that 30 yrs ago LOL.

              Comment

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