Editing Rifle (section)

===Bullet rotational speed (RPM)===

Bullets leaving a rifled barrel can spin at a [[rotational speed]] of over 100,000 revolutions per minute (rpm) (or over about 1.67 kilohertz, since 1 RPM = 1/60&nbsp;Hz). The rotational speed depends both on the [[muzzle velocity]] of the bullet and the [[Twist rate|pitch]] of the rifling. Excessive rotational speed can exceed the bullet's designed limits and the inadequate centripetal force will fail to keep the bullet from disintegrating in a radial fashion.<ref>{{cite web|title=Topic of the Month: July 2001 – Twist Rate |url=http://www.loadammo.com/Topics/July01.htm |work=Load From A Disk |access-date=26 August 2010 |url-status=dead |archive-url=https://web.archive.org/web/20130512015023/http://www.loadammo.com/Topics/July01.htm |archive-date=12 May 2013 }}</ref> The rotational speed of the bullet can be calculated by using the formula below.

*MV/ twist rate = rotational speed

Using metric units, the formula divides the number of millimeters in a meter (1000) by the barrel twist in millimeters (the length of travel along the barrel per full rotation). This number is then multiplied by the muzzle velocity in meters per second (m/s) and the number of seconds in a minute (60).
*MV (in m/s) × (1000&nbsp;mm /twist) × 60 s/min = Bullet RPM
For example, using a barrel that has a twist rate of 190&nbsp;mm with a muzzle velocity of 900&nbsp;m/s:
*900&nbsp;m/s × (1000&nbsp;mm /(190&nbsp;mm)) × 60 s/min = 284&nbsp;210 RPM

Using imperial units, the formula divides the number of inches in a foot (12) by the rate of twist that the barrel has. This number is multiplied by the muzzle velocity (MV) and the number of seconds in a minute (60). For example, a bullet with a muzzle velocity of {{convert|3000|ft/s|m/s}} leaving a barrel that twists once per foot (1/12") would rotate at 180,000rpm.<ref>{{cite web|title=Calculating Bullet RPM – Spin Rates and Stability|url=http://accurateshooter.wordpress.com/2008/06/03/calculating-bullet-rpm-spin-rates-and-stability/|work=AccurateShooter.com|access-date=26 August 2010}}</ref>
*MV (in fps) × (12 in. /twist rate) × 60 s/min. = Bullet RPM
For example, using a barrel that has a twist rate of 1 turn in 8" with a muzzle velocity of 3000&nbsp;ft/s:
*3000 fps × (12"/(8"/rotation)) × 60 s/min. = 270,000 RPM