Free recoil denotes the translational kinetic energy (Et) imparted to the shooter of a small arm when discharged and is expressed in joules (J), or foot-pound force (ft·lbf) for non-SI units of measure.
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 comfort level of a shooter's ability to tolerate free recoil is a personal perception.
Where as: Etgu is the translational kinetic energy of the small arm as expressed by the joule (J).
Projectile: of spitzer type, weighing 9.1 grams (140 grains), with a muzzle velocity of 823 meters per second (2,700 feet per second).
The momentum short form: and with the numeric values in place; From the momentum long form in both Imperial units of measure and in an English Engineering format: Whereas: Etgu is the translational kinetic energy of the small arm as expressed by the foot-pound force (ft·lbf).
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.