Trouble Matching bullet drop

Discussion in 'Long Range Hunting & Shooting' started by curiousaussie, Oct 18, 2010.

  1. curiousaussie

    curiousaussie Active Member

    Messages:
    27
    Joined:
    Dec 22, 2008
    G'day,

    Have been having trouble for weeks and weeks matching my 600m (660yards), 900m (1000yards), and 1000m (1100yards) bullet drops with the ballistics programs.

    The load is 60.5gn 2213SC pushing a 180gn Berger at 2820fps.

    When dialled in at 600m my shots at 1000m would be 4-5 clicks flatter than what any program said. Vice versa when dialled in at 1000m it would be out by 4-5 clicks at 600m.

    Was tearing my hair out trying to manipulate velocity an/or BC to get it to fit. No luck.

    This weekend just gone shot a five shot group at 1000m measuring 10.5 inches wide by 4.5 inches height. Was wrapped with the rifle but still didn't match up at 600m.

    Then I tried something different. I changed the clicks on the program from 0.1 mRad (scope a Nightforce 5.5-22x56 MLR metric) to 0.104mRad and suddenly 600m, 900m, and 1000m results matched the bullet's path.

    Has anyone had any experience with some scopes being not quite true to their click values?

    Or has anyone used the method of changing the click value in Exbal, JBM, or BulletFlight to make the trajectory fit the scope?

    Any advice would be greatly appreciated.

    Cheers,

    Matt
     

  2. J E Custom

    J E Custom Well-Known Member

    Messages:
    7,257
    Joined:
    Jul 29, 2004
    Matt.
    The G7 Ballistic coefiecent of the Berger is a closer match than the G1 so try using the G7 and
    the drops will be closer to the real thing.

    Also scopes do have a little error from MOA to inches and if they are near the limit of their
    turret travel there is more error because of thread clearance.

    J E CUSTOM
     

  3. rbkeiser

    rbkeiser Member

    Messages:
    16
    Joined:
    Nov 11, 2007
    If you make a grid graduated in MOA and look at it through a solid mounted scope at 105 yds, then click up through one or two turret revolutions you will likely get a big surprise. .25 MOA clicks are often not. I've seen them from .25 to .3 and everything in between. Not at all important if you know this but does confuse someone who hasn't observed it before. Also makes a significant difference at long range which you quickly realize once you've done the math.
     
  4. curiousaussie

    curiousaussie Active Member

    Messages:
    27
    Joined:
    Dec 22, 2008
    JE,

    Tried all various combinations of G1, G7, and Litz BC's to no avail.

    Scope has 20 MOA base so should be in the middle of its travel.

    rb,

    I think my scope is one of those i.e. it moves 1.04 cm per click rather than 1.00 cm, because once I changed the ballistics programs to 0.104mRad values then 600m, 900m, and 1000m come up all fit the actual bullet trajectory.

    Thanks,

    Matt
     
  5. RMulhern

    RMulhern Well-Known Member

    Messages:
    796
    Joined:
    Jan 2, 2003
    Gadjets!!