Miller Twist Rule

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Equation / Last modified by AndrewBudd on 2019/07/22 17:12
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The Miller Twist Rule is used to calculate the optimal barrel twist rate for stabilizing a bullet's flight given the bullet's diameter(D), length(L) and mass (m) . The resulting twist rate is the length in which the rifling of the barrel will make one full rotation. 

INSTRUCTIONS: Choose units and enter the following:

  • (D) the bullet's diameter 
  • (L) the bullet's length 
  • (m)  the mass of the bullet

Optimal Barrel Twist Rate (TR): The calculator computes the length  for one complete rifling rotation in inches.  However this can be automatically converted to other length units via the pull-down menu.

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The Math / Science

The Twist Rate is commonly written as a ratio. Some common rifling ratios are 1:7, 1:9, 1:36, where 1:7 corresponds to 1 turn in 7 inches.

Here is an interesting article on why proper bullet stabilization matters:


Further Information: