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How many RPM's is a bullet rotating fired out of a barrel with a 1:10 twist at 2700fps ? I came up with 3240 times per second or

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  • How many RPM's is a bullet rotating fired out of a barrel with a 1:10 twist at 2700fps ? I came up with 3240 times per second or

    How many RPM's is a bullet rotating fired out of a barrel with a 1:10 twist at 2700fps ? I came up with 3240 times per second or 194,400 PPM's am i correct?

  • #2
    I come up with the same numbers. 2700fps X 12" = 32,400 ips divided by 10" = 3240 rps X 60 = 194,400 rpm.
    I do not have the formula for this, so I'm using common analysis and everyday math skills.
    I hope we're right.

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    • #3
      Close enough. Anything you hit with said bullet will not care about the rpms.

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      • #4
        Ditto~99 +1

        Close Enough.

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        • #5
          No wonder the old .223 rifles with 1:9 twist would not stabilize the heavy bullets. I did a comparison and it takes 16% more revolutions to stabilize a 75gr in 1:7 twist over the 55gr in the 1:9 twist. I had a rifle with the 1:9 and it would keyhole the heavy ones.
          The difference in the example is 705 feet per second increase in revolution for the 75gr. Just curious.

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          • #6
            Also, at a lower velocity, the heavier bullets would have a slower rpm twist.

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            • #7
              99explorer
              the example i used was
              55gr 3200 velocity 1-9 twist revs per second 4266
              75gr 2900 velocity 1-7 twist revs per second 4971

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              • #8
                The math checks out, without rounding up for fractional differences.
                Can we assume the 1-7 twist at 2900fps stabilizes the 75-grain .223 bullet?
                I have a friend with the same problem.

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                • #9
                  i used 75gr in the example, heaviest i have loaded is 62gr and they shoot fine.

                  Comment

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