6.5 Grendel TC Contender

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  • JASmith
    Chieftain
    • Sep 2014
    • 1620

    #46
    Several techniques exist for optimizing one's OAL. Here is what I use:
    • Start out by finding the OAL where your ogive first touches the lands.
    • Then, back off by the Barnes recommended amount.
    • Do an OAL ladder using a slightly reduced from max load. Run the OAL in increments of .005" to .010" from that recommended .050" down to touch to determine the most accurate OAL. The reduced load is suggested because getting close to or actually touching the lands causes an increase in pressure of a few thousand psi.
    • Repeat with five five-shot groups with OALs .006", .003', 0.00', -.003' and -.006" from your best OAL in the first pass.

    If your SSK barrel was cut with a SAAMI-compliant reamer, the 0.50 degree taper where the freebore normally would be broadens the sweet spot for best accuracy and at the same time makes getting the precises land-touch OAL more interesting.

    I normally run the powder charge weight optimization after I am happy with the OAL.
    shootersnotes.com

    "To those who have fought and almost died for it, freedom has a flavor the protected will never know."
    -- Author Unknown

    "If at first you do succeed, try not to look astonished!" -- Milton Berle

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    • Joseph5
      Warrior
      • Oct 2012
      • 370

      #47
      The parent case for the 6.5 JDJ was the 225 Winchester if I am not mistaken, which I could be, the memory isn't what it used to be.

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      • JASmith
        Chieftain
        • Sep 2014
        • 1620

        #48
        Originally posted by Joseph5 View Post
        The parent case for the 6.5 JDJ was the 225 Winchester if I am not mistaken, which I could be, the memory isn't what it used to be.

        The 6.5 JDJ gas a .473" rim diameter and about eight nore graind of case capacity.
        Last edited by JASmith; 10-20-2016, 07:55 PM.
        shootersnotes.com

        "To those who have fought and almost died for it, freedom has a flavor the protected will never know."
        -- Author Unknown

        "If at first you do succeed, try not to look astonished!" -- Milton Berle

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        • hhi812
          Unwashed
          • Oct 2016
          • 5

          #49
          Thanks for the info. What did you mean,"I normally run the powder charge weight optimization after I am happy with the OAL."

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          • JASmith
            Chieftain
            • Sep 2014
            • 1620

            #50
            As I recall a lot of the afvice is to get your most accurate powder charge, then tweak the COAL.

            My own experience has been that I get larger group size swings by changing the COAL. So, for me, it seems sensible to take care the big one first, then tweak the charge weight.

            The problem with either approach is that we are dealing with both barrel vibrations and jump. The jump affects both the alignment of the bullet entering the throat and the timing. The powder weight largely effects the time to bullet exit.

            If one were serious about the best accuracy (I cannot claim to be since I am thrilled when the groups drop below 0.5 moa) then running through both to verify the sweet spot in both dimensions might be advisable.
            shootersnotes.com

            "To those who have fought and almost died for it, freedom has a flavor the protected will never know."
            -- Author Unknown

            "If at first you do succeed, try not to look astonished!" -- Milton Berle

            Comment

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