Rifling - Twist Rate - Bullet Revolutions Per Minute (rpm)

Bullet Revolutions Per Minute (rpm)

A bullet fired from a rifled barrel can spin at over 300,000 rpm, depending on the bullet's muzzle velocity (MV) and the barrel's twist rate.

The general formula for calculating the rpm of a rotating object may be written as

where is the linear velocity of a point in the rotating object (in units of distance/minute) and C refers to the circumference of the circle that this measuring point performs around the axis of rotation.

For a bullet, the specific formula below uses the bullet's MV and the barrel's twist rate to calculate rotational speed:

  • MV(in fps) x (12/twist rate in inches) x 60 = Bullet rpm

For example, a bullet with a muzzle velocity of 3050 ft/s fired from a barrel with a twist rate of 1 in 7-inch (180 mm) (e.g., the M16A2 rifle) spins at 313,714 rpm.

Excessive rotational speed can exceed the bullet's designed limits and the resulting centrifugal force can cause the bullet to disintegrate in a radial fashion.

Read more about this topic:  Rifling, Twist Rate

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