Please help with my trajectory

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by SmoakAllen, Dec 7, 2006.

  1. SmoakAllen

    SmoakAllen Member

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    I used a free ballistic trajectory program called www.eskimo.com. I plugged in all the information. I am shooting a .300RUM with a 165grain bullet and 100gr of RL25 in a 31" barrel. I sight the rifle in at 100 yards and it is dead on, a 3 shot group making one ragged hole. After cleaning the barrel I look at the trajectory program and it says to adjust 9 clicks (1/4 moa) for 300 yards. I shoot a group measuring 1.5" off the mirror of my truck. However the group is about 2 inches to the right and about 4 inches high. I can see it being to the right becuase of a slight wind but I dont see why it is so high. So I back off to 350 yards and adjust the scope a total of 12 clicks. The same exact thing happens only with the group measuring 1.75". Why is it that I am hitting so high. Please give your opinions.
     
  2. MagMan

    MagMan Well-Known Member

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    Are you positive your velocity, ballistic coefficient, and altitude are correct?

    and are you also sure you don't have 1/2 MOA clicks on your scope?
     

  3. Buffalobob

    Buffalobob Writers Guild

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    I suggest you use a better rest than a truck mirror to check your drops. You are probably getting a "bounce" from the mirror.
     
  4. SmoakAllen

    SmoakAllen Member

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    The mirror was a very stead rest, I was shooting decent groups, for me at least. And I am not sure of the velocity since I do not have a chronograph, but I am guessing 3600fps. My scope is 1/4 it is a Leupold 6.5-20x50 LR
     
  5. edge

    edge Well-Known Member

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    [ QUOTE ]
    The mirror was a very stead rest,

    snip

    [/ QUOTE ]

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  6. CatShooter

    CatShooter Well-Known Member

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    Between not knowing the velocity, and the possible errors on BC (many are not accurate, or not for use in the program you are using)... it is easy to have that much error at 300 yds.

    For example, Hornady BC are usually less than what their flight path will actually be, so program predictions are lower than actual flight paths.

    And even Sierra (who supposedly tests each bullet) are often off enough to make a difference to a Prairie Dog shooter.

    .
     
  7. zingdingo

    zingdingo Well-Known Member

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    I never had much luck getting ballistic charts to match reality closely until I got a chronograph. Trying to juggle uncertain B.C. and velocity at the same time is a tricky game at best.
     
  8. flims

    flims Active Member

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    Oct 18, 2006
    check that you scope tracks exactly the amount advertised, it could be repeatable but slightly off the advertised amount. ideally you check this at 100m/yards and dial in 2 MOA for a series of 5 shots. they should be an inch apart. shot your return to zero and dial in 14MOA this time and measure the high of the point of impact from point of aim.

    I would suggest you dont count clicks otherwise you never make the shot in non range type scenario. work in full MOA or fractions of thereof.
    once this is done get those loads chronoed, unless you have this you cannot get anything square or close with software.