Muzzle energy
Muzzle energy is the kinetic energy of a bullet as it is expelled from the muzzle of a firearm. It is often used as a rough indication of the destructive potential of a given firearm or load. The heavier the bullet and the faster it moves, the higher its muzzle energy and the more damage it will do.
The general formula for the kinetic energy is:
- E = 0.5 • m • v2
In SI units, mass m is in kilograms and velocity v is in metres per second, giving kinetic energy E in joules.
When using a system of units that is not self-consistent, or if the weight of the bullet is used rather than the mass, a conversion factor must be added. For example, to get muzzle energy E in foot-pound force, where
the formula is
- E = m • v2 / (2 • 32.1739 • 7000).
Most sporting arms publications within the United States report muzzle energies in foot-pound force, and, when publishing kinetic energy tables for small arms ammunition, use a dimensional constant of 32.163 lbm • ft / lbf • s² rather than the standard acceleration of gravity of 32.1739 ft / s².
The bullet energy, remaining energy, down range energy and impact energy of a projectile may also be calculated using the above equations.
Typical muzzle energies of common firearms and cartridges
Typical muzzle energy levels of different types of firearms for both SI units (joules) and English Engineering System units (foot-pound force) are:
Firearm Caliber Muzzle energy (ft • lbf) (J) air gun .177 5 7 rifle .22LR 100 135 rifle 5.56x45 mm 1200 1550 pistol (semi-auto) 9 mm 350 540
Average muzzle energies E in foot-pounds for common pistol cartridges:
Cartridge E 9 mm Luger 350 .357 Sig 475 .357 Mag 550 .38 Special 200 10mm Auto 650 .40 SW 425 .44 Mag 1000 .45 GAP 350 .45 ACP 370 .45 Colt 370 .454 Casull 1900 .460 SW 2400 .50 AE 1500 .500 SW 2600
Resources
Edward F. Obert, Thermodynamics, McGraw-Hill Book Co., 1948.
Mc Graw-Hill encyclopedia of Science and Technology, volume ebe-eye and ice-lev, 9th Edition, Mc Graw-Hill, 2002.
