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 (E_t) imparted to the shooter of a small arm when discharged and is expressed in joule (J) and foot-pound force (ft·lb_f) 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.