Different shape boattails effect on BC

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by Cold Trigger Finger, Nov 2, 2013.

  1. Cold Trigger Finger

    Cold Trigger Finger Well-Known Member

    Messages:
    845
    Joined:
    Nov 2, 2012
    How much effect do the different shape boattails have on ballistic coeffeficency??
    Do rebated boattails have a greater effect than a straight taper. ?
    Thank you.
     
  2. Mikecr

    Mikecr Well-Known Member

    Messages:
    4,269
    Joined:
    Aug 10, 2003
    There are sweet spots to boat tail angle.
    An example with angle changes to 6mm 105 Lapua,while holding same weight:
    BTA= angle
    BCbyED= ICAO G1 BC @ 3Kfps by angle changing end diameter
    BCbyBTL= ICAO G1 BC @ 3Kfps by angle changing boat tail length

    BTA BCbyED BCbyBTL
    4 0.485 0.513
    5 0.490 0.506
    6 0.493 0.500
    7 0.495 0.495
    8 0.495 0.490
    9 0.494 0.485
    10 0.492 0.481
    11 0.489 0.477
    12 0.486 0.474
    (do know how to space)
    There there can be an angle with the best overall balance in origin. Lapua chose 7deg.
    The trend holds but shapes differently at other velocities and air densities.

    I can't calculate rebated boat tail results. They do not increase BC over linear angles, and if I remember right Litz found they did not hurt BC much if any either.
    The benefit they seek is in accuracy from cleaner release at the muzzle.
     

  3. Cold Trigger Finger

    Cold Trigger Finger Well-Known Member

    Messages:
    845
    Joined:
    Nov 2, 2012
    OK. Thanks. . My goal is to find the best combination for my fur bullet. . As most predators are taken at 300 yards or less I want a bullet that will be stabil at close range but also be stable at long range. So I'm kinda looking for a unicorn. . Its easy to find target or big game bullets but not so easy to find what I'm after.
    So, I'm hoping to get some educating.