What is the significance of rifling rate of twist?

Explanation of Twist rate

The rate/frequency of a barrel’s rifling spirals determine what bullet weights will be best stabilized in flight, and will therefore offer the best accuracy. Twist rate is expressed as the barrel length required for the projectile to make one complete revolution. For example, 1:10, or 10", is "one turn in ten inches."

Given the same bullet diameter, lighter bullets require a slower rate of twist and heavier bullets require a faster rate of twist. Listed below, by caliber, are common and specialty barrel rifling twists along with the bullet weights they are typically used with.

Optimum rates of twist can be calculated by the Greenhill Formula:

C = 150 (180 for muzzle velocities exceeding 2,800 f/s)

D = bullet's diameter (inches)

L = bullet's length (inches)

SG = bullet's specific gravity

The Miller Formula may also be used:

m = bullet mass by grain

s = gyroscopic stability factor

d = bullet diameter (inches)

l = bullet length

t = twist in calibers per turn

Note: Beretta, Sako and Tikka firearms utilize rifling twists that are optimum for the caliber and configuration of the firearm. The following list is for informational purposes only, and does not represent the twists available from Beretta, Sako and Tikka at any given time. Beretta, Sako and Tikka will not accept orders for twist rates other then what is listed in the current product catalog. The twist rates shown are typical for smokeless powder cartridges. Please click on these links to get the current rates of twist and technical data for Sako and Tikka rifles.

Twist