Free recoil is a vernacular term or jargon for recoil energy of a firearm not supported from behind. Free recoil denotes the translational kinetic energy imparted to the shooter of a small arm when discharged and is expressed in joules, or foot-pound force for non-SI units of measure. More generally, the term refers to the recoil of a free-standing firearm, in contrast to a firearm securely bolted to or braced by a massive mount or wall. Free recoil should not be confused with recoil:
Free recoil is the given name for translational kinetic energy transmitted from a small arm to a shooter.
Recoil is a name given for conservation of momentum as it generally applies to an everyday event.
Free Recoil and Firearms
Free recoil, sometimes called recoil energy, is a byproduct of the propulsive force from the powder charge held within a firearm chamber or breech. The physical event of free recoil occurs when a powder charge is deflagrated within a firearm, resulting in the conversion of chemical energy held within the powder charge into thermodynamic energy. This energy is then transferred to the base of the bullet and to the rear of the cartridge or breech, propelling the firearm rearward into the shooter while the projectile is propelled forward down the barrel, with increasing velocity, to the muzzle. The rearward energy of the firearm is the free recoil and the forward energy of the bullet is the muzzle energy. The concept of free recoil comes from the tolerability of gross recoil energy. Trying to figure the net recoil energy of a firearm is a futile endeavor. Even if you can calculate the recoil energy loss, due to:
the factors of human perception are not calculable. Therefore, free recoil stands as a scientific measurement of recoil energy, just as the room or outside temperature is measured. The comfort level of a shooter’s ability to tolerate free recoil is a personal perception. Just as it is a person's personal perception of how comfortable he or she feels to room or outside temperature. There are many factors that determine how a shooter will perceive the free recoil of a firearm. Some of the factors are, but are not limited to:
There are several different ways to calculate free recoil. However, the two most common are the momentumshort and long forms. Both forms will yield the same value. The short form uses one equation as where the long form requires two equations. With the long form you will first find velocity for the fire arm. With the velocity known for the small arm, the free recoil of the small arm can be calculated using the translational kinetic energy equation.
Momentum short form:
Momentum long form: →
Where as: Etgu is the translational kinetic energy of the small arm as expressed by the joule. mgu is the weight of the small arm expressed in kilograms. mp is the weight of the projectile expressed in grams. mc is the weight of the powder charge expressed in grams. vgu is the velocity of the small arm expressed in meters per second. vp is the velocity of the projectile expressed in metersper second. vc is the velocity of the powder charge expressed in meters per second. 1000 is the conversion factor to set the equation equal to kilograms.
Projectile: of spitzer type, weighing 9.1 grams, with a muzzle velocity of 823 meters per second. Powder charge: single base nitrocellulose, weighing 2.75 grams, with a powder charge velocity of 1,585 meters per second. The momentum short form: and with the numeric values in place;
For non-SI units of measure of energy see Foot-pound force. The conversion is: 1 J = 0.737 562 ft·lbf
Where as: Etgu is the translational kinetic energy of the small arm as expressed by the foot-pound force. mgu is the weight of the small arm expressed in pounds. mp is the weight of the projectile expressed in grains. mc is the weight of the powder charge expressed in grains. vgu is the velocity of the small arm expressed in feet per second. vp is the velocity of the projectile expressed in feet per second. vc is the velocity of the powder charge expressed in feet per second. gc is the dimensional constant and is the numeral coefficient of 32.1739 7000 is the conversion factor to set the equation equal to pounds.
The following free recoil energy table does not take into consideration: recoil suppression devices, or loss of energy due to auto loading mechanism. English units of measure are enclosed in parentheses.
