The power factor of a cartridge is calculated by multiplying its bullet weight (in grains) by its velocity (in feet per second) and then dividing the result by a constant factor, typically 1,000. The power factor is often used in shooting sports, such as IPSC (International Practical Shooting Confederation), to determine the minimum power level required for ammunition used in competitions.
7.62x51mm (.308 Winchester): The bullet weights commonly used in the 7.62x51mm cartridge range from around 147 to 180 grains (9.5 to 11.7 grams). Typical muzzle velocities for these bullets are around 2,600 to 2,800 feet per second (790 to 850 meters per second). Therefore, the power factor for 7.62x51mm (.308) ammunition would be approximately 380 to 504.
7.62x54mmR: The bullet weights used in the 7.62x54mmR cartridge can vary from around 147 to 203 grains (9.5 to 13 grams). Muzzle velocities for these bullets typically range from 2,600 to 3,000 feet per second (790 to 910 meters per second). Consequently, the power factor for 7.62x54mmR ammunition would be approximately 380 to 610.
Please note that the power factor can vary depending on the specific load and bullet weight used within each cartridge. The values provided here are general estimates to give you an idea of the power factors commonly associated with these cartridges.