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

v is the velocity of bullet (in feet per second)

m is the mass of bullet (in grains)

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 lb_m • 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

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.

See also

• muzzle velocity
• firearm
• foot-pound force
• free recoil