Bullet drop is low at mid range and high at long range??

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  • Bullet drop is low at mid range and high at long range??

    G’day, this is my first post and I’m after some help with the bullet drop difference between my ballistic calculator and measured bullet drop. I’ve set up my Howa 1500 308W, shot in the barrel, load tested factory ammo to find one that works well and zeroed it. I checked the scope level and have a cant bubble. Set up the ballistic calculator and checked the drop data on paper 3 times out to 600m. I’m getting 0.8MOA vertical spread in my groups consistently even out to 600m (I haven’t got reading the wind right yet). My zero is at 30m and 210m. 15cm PBR is 250m. At 350m my groups are 2MOA low from the B-Calc and at 600m are 2MOA high. This seems to defy gravity as a constant? Can you give me any advice on what I’m missing or getting wrong?
    Ammo: Hornady Superperformance 165gr SST
    B-calc: Lapua App

  • #2
    I can't help with the app or calculations, but my advice is to trust and have faith in what the bullet is doing in real life rather than theoretical calculations
    I work so that I can live, not live so that I can work.

    Comment


    • Horsbuc
      Horsbuc commented
      Editing a comment
      Thanks scruffy bob! Agree on trusting the bullet… it does seem to know what it’s doing.

  • #3
    I was surprised how accurate the basic apps are at the medium ranges I shoot to, 600m so far.

    As long as the data entered is correct, they seem to work.
    Speed is crucial and correct bullet BC helps.

    I have used basic free apps like Hornady and the better Streloc pro paid app.

    If they exaggerate the speed and BC figures on the ammo box writings, search them out online.

    Comment


    • Horsbuc
      Horsbuc commented
      Editing a comment
      Thanks magoo, I’ll check out the Hornady app.

  • #4
    Hi Horsbuc and welcome to the forum.
    what you're experiencing is not that uncommon and i have experienced it myself several times.
    there were times when i would have to do the following;
    test my point of impact at 100m, 300m, and 600m.
    find out how much real world drop i was getting, then enter or adjust different speed figures into the ballistics apps until i found the speed that matched my real world results.
    this would then give me enough data to use at all the other distances.
    works for me.

    what are you using your rifle for? hunting or target use?

    Comment


    • Horsbuc
      Horsbuc commented
      Editing a comment
      Thanks Send-it, I write my shooting data in a range journal… range, weather, app calculations and actual turret adjustments, group, POI deviation from zero and any notes. I’ll compare the Hornady app data and adjust the muzzle velocity in both to see if I can get it to line up. I’m hunting out to PBR distance, but not further. Targets out to 600m. Can’t go further than that until I’m better at reading the wind…

  • #5
    Not sure on the lapua app but the hornady app needs the axial form factor (whatever that is...) to be set but you need to gather info on dial up at various ranges then set app to match
    "If you think you are too small to make a difference, try sleeping with a mosquito."

    Comment


    • Horsbuc
      Horsbuc commented
      Editing a comment
      Thanks Savage 7mm, I’ll give the Hornady app a try.

  • #6
    try the berger ballistics web page.
    its handy.

    Comment


    • #7
      Originally posted by Horsbuc View Post
      G’day, this is my first post and I’m after some help with the bullet drop difference between my ballistic calculator and measured bullet drop. I’ve set up my Howa 1500 308W, shot in the barrel, load tested factory ammo to find one that works well and zeroed it. I checked the scope level and have a cant bubble. Set up the ballistic calculator and checked the drop data on paper 3 times out to 600m. I’m getting 0.8MOA vertical spread in my groups consistently even out to 600m (I haven’t got reading the wind right yet). My zero is at 30m and 210m. 15cm PBR is 250m. At 350m my groups are 2MOA low from the B-Calc and at 600m are 2MOA high. This seems to defy gravity as a constant? Can you give me any advice on what I’m missing or getting wrong?
      Ammo: Hornady Superperformance 165gr SST
      B-calc: Lapua App
      It sounds like you may have your velocity set way too high did you add an extra zero to the velocity on the chart?

      Comment

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