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Spinning Bullets

Discussion in 'The Powder Keg' started by BattleRifleG3, Mar 23, 2002.

  1. BattleRifleG3

    BattleRifleG3 Retired Moderator

    Ok, my friend and I went shooting his AR-180 today, and when we looked at the targets, the hits had the distictive "keyhole" shape of tumbling bullets. We'd seen it before when shooting through multiple layers of targets, but this was a clear shot. The bullets used were 62gr FMJ boat-tail and SS109, both facory and handloads with 25gr of IMR 4320. We figured it was because of the 1/12 rifling of the 180, as I'm told the SS109 should use 1/7 rifling. Anyone know more about this?
     
  2. rajohns

    rajohns G&G Newbie

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    wis.
    Yes the problem is caused by the 1/12 rifling. You would need 1/10 to1/7 to stablize 62 gr. bullets. 55gr. should shoot fine though.
     

  3. AR-tim

    AR-tim G&G Newbie

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    WI
    How did the SS109(green tip stuff, right?) work for you? Besides the bullets tumbling, how did it function? I have been thinking about buying some and haven't heard much feedback.
     
  4. m14nut

    m14nut G&G Newbie

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    NJ
    It's your rifling, 1/12 will stabilize up to about 57gr. If 55gr. bullets are not keyholing and 62's are it's definitely a stabilization problem.
    The ss109 will shoot fine in 1/9 twists and faster. 1/7's have been known to separate 52gr and lower weight bullets due to over-rotation.
    Have owned about 6 different configs. of the AR, have found that for just plinking, stick with 55's. Match shooting: 1/9, 52gr. Horn Match and 68gr. Horn match <or> 69gr. Sierra match.
    !/8's and 1/7's can stabilize the big 77 and 80gr. match bullets.:eek:
     
  5. j schwindler

    j schwindler G&G Newbie

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    You don't really need a 1/7 twist. That twist rate was designed for arctic conditions where stabilization requires a faster twist rate in the low temperature(look up the stabilization equations) and also for the M856 tracer which is longer than the M855 (ss109) round.

    J Jacob Schwindler, Attorney at Law
     
    Last edited: Mar 27, 2002