Barrel twist rate= Effects big/small

HeavyAssault

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  • Feb 14, 2011
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    When selecting barrel twist rates I realized there are often the good ol' stand by, but what about the other offerings.
    As example: A 1-8.0 TR compared to a 1-7.5 TR

    My perceptions for TRs this close together:
    It is reasonable to say that small of a TR change is purely for those trying to squeeze out the 99.9% most of their setup.
    >Example: The average guy isn't going to see the difference on paper or while on the hunt.
    It is really just going to effectively cause the selection of "best" bullet weights to change.
    >Example: Instead of using 140gr bullets, one must use 143gr bullets for consistently better results.

    I'd know this is going to vary across calibers so I left that specific part out. I'm just trying to get the basic understanding of how this small of a change makes a difference large or small. Thanks in advance.
     

    Edds

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    Jan 19, 2012
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    If an 8.0" twist will stabilize your bullet, a 7.5" twist will work fine.

    If it takes a 7.5" twist to stabilize your bullet, an 8.0" twist will not work fine.
     

    Reload10

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    Jan 21, 2018
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    Subscribe to Applied Ballistics and you will have all your questions and theorys answered. Eliminates the internet bull shit.

    Also, look at Miller Stability formula for what twist your particular cup and core bullet requires.
     

    spamassassin

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    It only takes a little extra length to drop the stability factor just enough to cost you all of the extra BC that the longer bullet gives you over a slightly shorter one. If you're at (as an example with made up numbers) 1.4Sg on an 8 twist and losing 4% of your BC because of that a 7.5 can pull you up to 1.5Sg and you get the full value. There's a lot more to it than that but just because your bullet doesn't turn sideways right out of the muzzle doesn't mean it's spinning fast enough to avoid nutation.
     
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