Ballistics
The motion of a projectile, from the instant of firing until impact at the target, is divided into three distinct phases: (1) interior ballistics, which treats of the motion of a projectile while it is still in the gun; (2) exterior ballistics, which considers the motion of the projectile from the time it emerges from the gun until it reaches the target; and (3) terminal ballistics, which deals with the effect of the projectile on the target.
If the gun and shooter are at rest, then the force on the bullet is equal to the force on the gun-shooter. This is due to Newton's third law of motion (For every action, there is an equal and opposite reaction). Consider a system where the gun and shooter have a combined mass M and the bullet has a mass m. When the gun is fired, the two objects move away from one another with new velocities V and v respectively. But the law of conservation of momentum states that their momenta must be equal. Since force equals the rate of change in momentum and the initial momenta are zero, the force on the bullet must therefore be the same as the force on the gun/shooter.
Hollywood depictions of firearm victims being thrown through plate-glass windows are inaccurate. Were this to be the case, the shooter would also be thrown backwards with equal force. Gunshot victims frequently fall or collapse when shot; this is less a result of the momentum of the bullet pushing them over, but is primarily caused by physical damage or psychological effects, perhaps combined with being off-balance.
Velocity
From Eq. 1 we can write for the velocity of the gun/shooter: V = mv/M. This shows that despite the high velocity of the bullet, the small bullet-mass to shooter-mass ratio results in a low recoil velocity (V) although the force and momentum are equal.
Kinetic Energy
However, the smaller mass of the bullet, compared that of the gun-shooter, allows significantly more kinetic energy to be imparted to the bullet than to the shooter.
The ratio of the kinetic energies is the same as the ratio of the masses (and is independent of velocity). Since the mass of the bullet is much less than that of the shooter there is more kinetic energy transferred to the bullet than to the shooter. Once discharged from the weapon, the bullet's energy decays throughout its flight, until the remainder is dissipated by colliding with a target.