Rifling - Twist Rate - Expressing Twist Rate

Expressing Twist Rate

Three methods are used to describe the twist rate.

The first and traditionally most common method expresses the twist rate in the length required to complete one full projectile revolution in the rifled barrel.
This method does not give an easy understanding if a twist rate is relatively slow or fast when bores of different diameters are compared.

The second method describes the length required to complete one full projectile revolution in calibers or bore diameters.

where:

  • Twist = twist rate expressed in bore diameters
  • L = the twist length required to complete one full projectile revolution in mm or in
  • Dbore = bore diameter (diameter of the lands) in mm or in

The third method describes the angle of the grooves relative to the bore axis in degrees.
The last two methods have the advantage that they express the twist rate as a ratio and give an easy understanding if a twist rate is relatively slow or fast even when comparing bores of differing diameters.

Read more about this topic:  Rifling, Twist Rate

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