at , set by an unnamed soldier with Canada's elite special operations unit Joint Task Force 2 using a McMillan TAC-50 sniper rifle. 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 Hz). The rotational speed depends both on the muzzle velocity of the bullet and the 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. 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 mm /twist) × 60 s/min = Bullet RPM For example, using a barrel that has a twist rate of 190 mm with a muzzle velocity of 900 m/s: 900 m/s × (1000 mm /(190 mm)) × 60 s/min = 284 210 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 leaving a barrel that twists once per foot (1/12") would rotate at 180,000rpm. 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 ft/s: 3000 fps × (12"/(8"/rotation)) × 60 s/min. = 270,000 RPM Caliber Rifles may be chambered in a variety of calibers (bullet or barrel diameters), from as low as 4.4 mm (.17 inch) varmint calibers to as high as 20 mm (.80 caliber) in the case of the largest anti-tank rifles. The term caliber essentially refers to the width of the bullet fired through a rifle's barrel. Armies have consistently attempted to find and procure the most lethal and accurate caliber for