Bullet stabilization question

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by SouthPawShooter, Aug 13, 2011.

  1. SouthPawShooter

    SouthPawShooter Well-Known Member

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    Apr 26, 2010
    Just got a custom Remington 700 calibrated in 6mm Ackley it has a 24" Douglas 1-10 twist, fluted in standard contour. My question is I want to try 2 Berger bullets one is the 6mm 88 Grain Match Varmint High BC FB which calls for 1-10 twist barrel for coyotes and fire forming then some Berger 6mm 95 Grain Match Hunting VLD which call for 1-9 twist in my Ackley loads for Deer. Do you think with a 24" barrel I can stabilize a 95gr in an Ackley load through a 1-10? Again this 95gr. bullet calls for a 1-9 twist barrel but this is for my Ackley load.
     
    Last edited: Aug 13, 2011
  2. Ridge Runner

    Ridge Runner Well-Known Member

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    Dec 13, 2002
    folks could run all the formula's, make they're best guesses, and feed yo a bunch of info, the fact is you won't know till ya try them.
    RR
     

  3. Mikecr

    Mikecr Well-Known Member

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    Aug 10, 2003
    Stabilization isn't directly about barrel length or load.
    That it's a larger 'Ackley load' isn't enough factor to concern over.
    And barrel length is not a direct matter in this, because regardless of it's length the twist rate is set at 1 turn per 10" of displacement. Do NOT think of stabilization in terms of RPMs because it fails more tests than Paris Hilton..

    Now indirectly both barrel length and load can affect stabilization, due to the potential for ugly bullet release, that has to be overcome by twist rate.
    If a 24" barrel is short for the load, you generate higher muzzle pressure(fireball), which slaps the back of a freely released bullet at angles(especially with boat tails). This acts like crown issues and it amplifies any crown issues.
    A supersonic bullet is least gyroscopically stable right at the muzzle, so if your twist isn't high enough bad results are set in motion right there(no matter where you notice them).

    If a bullet is unstable(Sg <1.0) it will tumble immediately even with perfect release.
    Marginally stable(Sg >1.0 but <1.5) would not tumble unless something challenges that condition to a point of being insufficient(like jacket failure or dynamic instability). But stability varies with conditions other than twist rate(bad crown, hi air density), so being marginal has it's risks.
    Fully stable(Sg ~1.5) gives you margin without hurting performance.

    Using the Miller rule of thumb for stability(for illustration) and my measurements of a 95grVLD,
    I get:
    Sg = 1.36 @ 3kfps, 9tw, under ICAO conditions
    Sg = 1.44 @ 3kfps, 9tw, @90deg
    Sg = 1.28 @ 3kfps, 9tw, @30deg

    Sg = 1.10 @ 3kfps, 10tw, under ICAO conditions [bad performance]
    Sg = 1.17 @ 3kfps, 10tw, @90deg
    Sg = 1.04 @ 3kfps, 10tw, @30deg [probably tumble]

    Sg = 1.16 @ 3500fps, 10tw, under ICAO conditions
    (so you can see that velocity is a minor factor)

    For my 95VLDs and 26" barrel chambered in 6BR:
    Sg = 1.52 @ 2975fps, 8.5tw, under ICAO conditions
     
    Last edited: Aug 13, 2011